Like -
Why are you leaving? (then dig into that)
Would we have been able to retain you?
What did you like about working here?
What did you not like about working here?
Basically that. And when they give criticisms if it's all because everyone else sucks and nothing like simply, "I wish I would have done x more often" or "I missed this early and it made it really hard". And if you think that is too much to ask, the best professionals do that and don't just make it about, "my boss sucks, this person sucks, this department sucks, if you would have just let me do what I wanted you would be billionaires". It's just simple humility. That's it.