Famous people are typically conscious of how they're portrayed in the press. So, over time they develop talking points that can be used to answer frequently asked questions. As a result, they're predictable. But, that's not why you go to see them speak. Otherwise, you'd just watch them on YouTube. I go to see them in person because I want to hear their opinion on things they haven't published yet.
Most people ask questions about current events, but these are precisely the questions that they're most likely to prepare for. If you do this, you're never going to learn anything new.
Thinking of insightful questions is hard. Try asking questions from previous news cycles. You're more likely to get candid responses when they're less well unprepared. You'll know that you've been successful if there's a longer pause before they answer.