I think this is a conversation that should evolve over time. For a new PhD student in the US, who might be beginning a 5 year program, "what do you want to do after you graduate" is a big question and they may not know yet. I think it's worth asking, because some students may know and of course the earlier they know, the earlier you can give them concrete advice. It might be useful for you to give them your perspective on the pros and cons of different, common options -- of course you can emphasize this is just your perspective and they should seek out other opinions as well, and you aren't telling them what to do or judging them on their decisions. But I think just providing a framework and emphasizing this is an important thing to be thinking about early on -- even if the student doesn't know exactly what they want to do -- is already being supportive.
But there are still intermediate steps that can seem more attainable and real and still are useful even if they don't know what they want to do after graduation right away. For example: "you should be thinking about giving a good presentation and networking at your first conference. What are ways you can prepare for that?" Or, later on, "you should start thinking about who might be able to write you letters, and what are some ways you could get other faculty to know your work." These smaller-scale career-development conversations can naturally become larger ones over time, by building trust and establishing a language.
And I think it is worth revisiting the question of long-term career goals with the student regularly, say every 6 months to a year even for students who had a clear answer on day 1, since plans may change (actually, in general, "career development" discussions can even be more frequent depending on your relationship with your students, although these might be about smaller scale issues than "after graduation" talks). As a student approaches graduation, they will start to have to grapple with whether to continue as a postdoc or pursue industry opportunities. They will also have more information about how they like academia and their field, and what their skills are. Students approaching graduation may not feel comfortable telling their advisor they are thinking of leaving academia; if you want to be supportive, then making it clear that you want to support them regardless of their decision can be extremely valuable. Showing them to career services is certainly one track, but if you have colleagues who have changed fields, then putting your students in contact with these colleagues is also very valuable, since it is very hard to get good information about non-academic jobs from within academia. And, on the other side, for students that want to pursue a postdoc and tenure-track position, there are many steps that are valuable to take before writing job applications that students might not think about; starting a conversation 6 months before job application season starts might help prevent common pitfalls.
Of course it is also on the student to act on advice and take responsibility, but I think my overall feeling is that if you want to be a supportive advisor, having these kinds of conversations regularly, and trying to be as non-judgmental as possible and letting the student find their path in their own time, are good ways to help guide a student develop their own career.