I suggest you:
Clarify with your advisor exactly what is expected of you as a supervisor.
Clarify (again with your advisor) what is expected of the BSc student working on this project.
Communicate with your advisor about the difficulties you are having with this student. I suggest framing it as "this student seems underprepared for successfully completing this project, and also may be unmotivated" rather than assuming that laziness is the problem here.
Follow your advisor's advice about what to do with this student.
From my understanding of your question, I would paraphrase the problem this way:
I am supervising a student who is doing many things that I am unpleasantly surprised by and not doing many things I would expect and prefer. So far I have been unsuccessful in getting this student's behavior to change. I am worried this student's behavior will reflect poorly on me or otherwise make it harder for me to achieve my own professional goals.
My suggestions are based on two observations: First, it can be very difficult to change another persons behavior. Second, it sounds like there are multiple other issues that you can address regardless of the BSc student's behavior, and addressing these issues may reduce or eliminate the need to try to change the BSc's student behavior (making it easier to solve the problems you face).
1. Clarify with your advisor exactly what is expected of you as a supervisor.
I am worried that a possible failure in his project will indicate that I am an incompetent supervisor.
This comment suggests to me that you are trying to solve your problem without a clear sense of what a solution looks like. Note, your goal here is success for yourself, and your success as a PhD student-level supervisor may not be contingent upon the success of the BSc student. You should clarify with your advisor (or your department, or whoever has assigned you to supervise these BSc students) exactly what they expect from you as a supervisor.
What is expected of you may be independent of whether the BSc student successfully writes a thesis. For example, if your advisor clarifies that you are only expected to available for short, weekly/biweekly meetings when the BSc student requests them and to pay attention and give constructive comments in those meetings, then it is very easy to meet your advisor's expectations, regardless of whether the student succeeds or not. (Potentially even regardless of whether the student schedules or attends these meetings.) Or, for example, if your advisor clarifies that yes, you were expected to choose a research question for this student to do, then (even if you do not want to do this) you now know what tasks you must accomplish to achieve what is expected of you.
Your advisor's expectations could be ill-defined or unreasonable, or they could be straightforward and far less of a time and energy burden than what you are experiencing with your current approach. Your uncertainty and concern about how the BSc student's success or failure reflects on you suggests you do not know these expectations, and I suspect this is contributing more to your frustration with the BSc student than you might realize. Clarifying the expectations of you is a problem that you can concretely solve without depending on this student to change his behavior.
(If you have already consulted your advisor, and know what is expected of you, then I recommend editing your question to provide that context.)
2. Clarify what is expected of the BSc student working on this project.
he expects ME to develop the subject as well as the research questions. I certainly don't want to tell him what to do.
Again, you can consult with your advisor (or whoever assigned you to supervise) to clarify what the student is expected to do. Is the student expected to meet with you a certain number of times during the project? Is the student expected to come up with a research question independently? Was he told these expectations? (Is there a syllabus, or a list of learning objectives for the thesis, as mentioned by user @Mark ?) Clarifying what the student is actually expected to do can put clear limits on how much effort you are expected to expend on this student, and will also be useful for talking to the student about his behavior.
3. Communicate with your advisor about the difficulties you are having with this student.
Let's go back to a hypothetical example: your advisor expects the student to come up with a research question independently and only expects you to be available for meetings and to pay attention and provide constructive feedback. In this case, you could share with your advisor that the student does not appear to be meeting the expectation of coming up with an independent research question, and that you have been consistently available for meetings but the student has not be attending them. Your advisor might then have suggestions for how to encourage the student to develop a topic, what resources might be useful teaching tools for the student, or perhaps explicitly tell you that you have done what you can and you don't need to spend even more time chasing this student down.
On the other hand, if you were expected to provide the research question, or demonstrate to the student how to choose a research question, then you know that the difficulty to communicate to your advisor about is the student's skipping scheduled meetings and otherwise not doing tasks that the student should be doing (while you get working on the tasks you did not realize you were expected to do).
Communicate about this student using more neutral descriptions of the student's behavior than you have used in this question.
When you communicate about the problems with this student, I suggest framing it as "this student seems underprepared for successfully completing this project, and also may be unmotivated for reasons that are unclear to me" rather than saying "this student is lazy."
An interpretation of laziness is "disinclination to activity or exertion despite having the ability to act or to exert oneself. It is often used as a pejorative..." Wikipedia. Because lazy is often used as a perjorative, when I hear a supervisor/mentor call their supervisee/mentee lazy, I (personally) consider it an unnecessarily unkind evaluation (adding a perjorative to what could have been an objective evaluation: "this student did not put effort into completing the project"). It makes me wonder if the supervisor/mentor is unkind to their supervisee/mentee in other ways, and that line of thinking damages their reputation in my eyes. Your advisor may not share my opinion (I've gotten the impression that decent number of people consider calling students lazy perfectly reasonable), but if you are uncertain about your reputation, I suggest erring on the side of using more neutral descriptions of the student's behavior.
Additionally, note that the definition of laziness is continent upon someone "having the ability to act or exert oneself", and the evidence you have provided does not convince me that this student currently has the ability to accomplish what is expected of him. To be clear, the evidence does not convince me that this student doesn't have the capability, just that I did not get enough evidence to convince me either way. Why is that?
he seemed to have no idea of what he needs to do...he asked me what a research question is
You mention in a comment that "Actually he DOES know how to conduct a research project since he has organised and conducted similar projects during his previous years in college (small scale research projects though)." This makes it all the more surprising that he asked you "what is a research question?" However, I attended a teaching workshop on helping students develop "mastery", and the lecturers discussed the issue of students needing to both learn a skill and also learn when (i.e., in what conditions) to use that skill.
So an alternative explanation to "laziness" is that he thinks that choosing a research question for a BSc thesis is a different, more stringent process than how he chose research questions for previous, smaller scale projects, and that he has to do things differently for the BSc. He might have expected you to teach him this "new" approach, or to do it for him, if you are an expert relative to him, and was surprised and uncomfortable when you made clear that you expected him to accomplish this task without additional instruction or assistance from you. If this student does not recognize that his previous skills and activities apply here, then the perhaps an important and helpful way to supervise him is to have a short conversation pointing out that yes, those previous skills apply, he should use them, and he should regularly bring his work to you and make the changes you suggest to slightly size up the project for BSc thesis-level expectations.
Second, your inferences about the student's capability should take into account that there could many factors unseen by you that affect this student's capability. As user @astronat mentioned, we are currently in a global pandemic, and many students are facing financial constraints, illness or death among their family or friends, loneliness, disruptions to productive routines, or general mental health strains that are making it difficult for them to work. Perhaps one or more of these issues are hindering the BSc student's ability to apply himself to this thesis. All of these issues could also be occurring even if we were not facing a pandemic. Either way, you do not know, and it will not help you to assume that this student is lazy based on the limited information you can see. I say it will not help you, because you have framed this problem as "how do I change this student's behavior," when there could be much more powerful forces leading the student to behave this way, and trying to push back against them could be an unsuccessful use of your time and energy and cause you even more frustration than you have already endured.
4. Follow your advisor's advice about what to do with this student.
This returns to step #1. Let's say you clarify your advisor's expectations of you, what the student is expected to do, communicate the difficulties you've considered, and then your advisor tells you that they do not expect you to change this student's behavior. That they expect you to be available if the student asks to meet for feedback and to document the student's progress, then you have a clear solution and now you can spend more time focusing on your own research, instead of spending time worrying that this student's lack of progress will hurt your academic reputation.
If your advisor expects more from you, then you will also have opened up the conversation to receive advice from your advisor about how to solve the problem, which can help improve your academic reputation as someone who seeks out and considers advice for how to improve your own performance (you've demonstrated it here with your question, but your reputation will be better helped if you advisor gets to see this, too). You may even be able to recruit your advisor to help with this student, rather than hold you completely accountable for a difficult situation. If you end up not liking your advisor's advice, or thinking it is wrong, then I'm sure many other answers here will give you alternative ideas. But knowing what is and is not expected of you sounds like the highest priority problem to solve, rather than hitting your head against the metaphorical wall of "getting the student to change his behavior."
