He has been reading a book that is related to the paper only in title.
This along with him not making progress might be a sign that he is missing pre-requisites. Maybe the paper requires mathematical tools he is not familiar, or has several words which are new to him.
Usually, I'd go with some assisted reading/reviewing. This is very harsh, so be careful and prepared before attempting.
Set up a meeting with plenty of time, explain that you'll be studying the paper and he should try to read and understand by himself first. Mark some time you know he should be calm (i.e. don't do it last hour of Friday or right after a difficult test, also make sure the student isn't hungry). Schedule at least two hours, but preferably have more allocated time on your schedule, and try to know that he'll be free after the scheduled time as well. Ask him to bring a laptop or have a computer in front of him at the meeting place.
Then, the strategy is to tell him to read the paper and interrupt him at least once per sentence asking for clarifications (what does this word mean? Can you rephrase this? Why is the author making this exception?). He should know that your are trying to measure gaps in his knowledge and habits, so tell him to be honest if he does not know anything and that it doesn't matter if that's the case (might be a particular poor strategy when dealing with people from a cultural background who have issues admitting they don't know something). The tense scenario will naturally keep him focused (though you should try to put him at ease).
When he doesn't know anything (I don't know this word!) you can either explain to him (and check if he understood) or say something like "and how would you look it up?" (that is why I've suggested leaving the computer close by). Very often, you'll notice he has poor googling skills, so you'll present him with some useful websites (Linguee comes to mind when dealing with translation issues, it is simple to use when you know it exists, but a student might not find it out by himself). Maybe you'll need to introduce him some book on the matter, and go through its index (some students may have only learned an important topic over classroom notes that he/she threw away, he might be unable to name a single book he could check some equation if needed be).
Additionally, this will reveal gaps in the student background, maybe there is a complete theory that is relevant to the paper but the student knows very little about (something like: "yes, you need to know trigonometry before learning calculus" or "Yes, you need to study electrodynamics before studying quantum mechanics"). Many elective courses try way too hard to remove pre-requisites for students, and then student simply don't know about things that should be the pre-requisite in any sane place. The process of asking for clarifications over each sentence usually reveals this kind of gaps.
Often, people read complex texts ignoring parts they don't really understand. Maybe because they expect that part to be clearer as the reading progresses, perhaps they think they'll get it with more context, or they just hope that weird word lies in a sentence that isn't actually important. This is a poor reading habit that almost everyone has at some degree. However, struggling students might take it to a whole new level of reading without understanding. Part of the idea is to identify when this is happening and forcing the student not to ignore too much of the text.
After a while doing so, you should:
- Have taught the student how to use some tools that you are used to, be he never heard about.
- Have provided him with good basic references if he needs them.
- Have identified topics you expected him/her to have mastered, but he/she actually knows little about.
- Improved his/her reading habits a bit.
Explain to him that this is not to be done often, as it is too much time consuming and stressing for both of you. Also, the whole point is to fill basic gaps, once they're filled, this tool should no longer be used. Over time, he should get better at identifying these gaps by himself, and asking for assistance as needed.
Another note on how to handle the student:
I have two other students who are working on similar topics and they get it.
Unless they have very similar backgrounds (i.e. same bachelor degree at same university) to the struggling student, the comparison is more likely to be unfair than otherwise. Even if just in your mind, avoid comparing colleagues directly, and specially never compare colleagues in front of them (or speaking to either).