Well..considering we don't know what you know, its going to be very difficult to figure out what you need to ask. The best way to build questions is take what you know, and figure out what you are really interested in
If he played football/baseball/cricket/rugby - what team, where, why,what position
If he likes to read - what kind of books, how often
If he likes to game - board, rpg, everything. Is he a GM/DM, what kind of gaming sessions does he like, his longest, his shortest
etc..etc..etc...
I don't really have any suggestions beyond taking what you know, finding something thats interests YOU about HIM and asking questions about it.