This is definitely a question you want to prepare for! The only way you could get it wrong would be if you don’t have any questions to ask. Try to prepare a few, just in case some are covered by your interviewer before you get a chance to ask. And try to be insightful, rather than asking basic questions you could have figured out on your own. You could ask about research opportunities, working with specific faculty, recent faculty or student publications, what career paths graduates have pursued… whatever it is that sparks your interest! This shows that you’re actively interested, perceptive and that you’ve done your reading.