If I were him, I would go to my manager

If I were him, I would go to my manager, explain why I need to learn from you and let my manager deal with you or your manager to decide whether you can help me.

If I were you, I would give a general idea if possible so he can help himself if he wants to. Based on what you said, it’s not your job to help him. It’s necessary to protect yourself, but being generous can also help you in the long run. Don’t always remember those times when you got backfired by helping others. Sometimes the COST of protecting yourself is just too expensive.