It depends....sometimes things come up during the interview and you can form your question based on topics that you discussed. I've mostly asked my interviewers how they feel the dynamic is between the faculty and students; like do they mostly have open-door policies, etc. If I'm at a loss, I just ask the interviewer about him/herself. If it's a faculty member, they love telling you about where they studied and what their career has been like. If it's a student interviewer, you can ask them about how they like the program, or where they plan to take their pharmacy career.
Bottom line is, there is no right or wrong question; just feel the vibe from your interviewer and keep it flowing like a conversation. But not asking a question could make you seem uninterested, so take it as an opportunity.