I have trouble coming up with questions as well. Mainly because I did extensive research on the schools before applying. So I've already know all I need to know before applying there. During the tour around the schools that comes with the interview, the other students asked questions, and usually don't have too many. And you know something, most of the answers to every freakin questions they asked can be found online. I've concluded that those students either are really lazy and didn't know much about the school, or they are kiss-ups.
During one of my interview session, one of the student keeps asking the tour guide all sort of questions. He asked him "how many students are in a class?"
"what's the percentage of students matching residency after graduation?", "What sort of classes are included in the curriculum?".
One might think that the student is really interested in the school, but to me, he just sounds lazy and unprepared.