What kind of questions do we need to ask in Skip level meetings?

This really depends on the person... but in my opinion AMAs are places where you could ask some questions that are a bit of curveball and not really a tactical thing related to the current set of priorities. I feel like these questions give valuable insights into how the person thinks.

1. Career questions. "How did you arrive at your position?" "What were the crucial moments in your career?" etc.
2. Why questions. "Why are we doing X project?" "Why do we have this particular team structure"?
3. Team/Org/Company questions. History of the team/company, if they are a long time member. Where they see the team and/or company in the next 2-5 years?

VP of Engineering David Pan made a great video about this topic here: How To Effectively Leverage Skip Level 1:1s

I recommend going through the linked resources in the description of that video as well!

...as I don't want to ask any stupid questions.

Don't worry about looking "stupid" - As long as the question comes from a good place and you ask it politely, there's no harm done and only potential upside. If you're relatively new to the company, you can also attach a preface like "I'm new here so apologies if this is a dumb question, but I was just curious about...". When you preemptively put that self-deprecation "shield" in place, it's really hard for the other party to be mean to you in response. I talk more about this communication tactic here: "How do you overcome the fear of asking stupid questions / bothering people when you need help?"