Well certainly it depends on what you are trying to find out. Does this have to do with career choice? Does it have to do with religion? Does it have to do with daily life in a monestary? You decide what you want to find out and then ask questions accordingly. Also ask open ended questions to give him a chance to talk about whatever interests him. He might surprise you.
It also depends on what monks these are. Some monks are famous for their bakeries and bread baking. Some monks are famous for breeding and training dogs. You do your research before you go talk to the man. That just shows some respect for the monk. In other words, don't waste his time. Make the time valuable to you both.