How do you choose what to focus on with structured mentoring?

It feels like current issues are too short term for this, unless it is a fundamental issue like no having enough domain knowledge. Googling and/or a quick discussion with your colleagues should suffice in most cases.

If it is a more general subject, how to choose which one? Obviously there are a lot of things I don't know, but it's quite hard to pinpoint what would be the most beneficial thing to learn right now; otherwise I would have researched it already.

Maybe reviewing the recent work with the mentor, and trying to extract pain points from there could work?