Ask about skip-level one-on-ones, open door policies, watch their facial expressions when you ask. If they look away, make note of what direction their eyes move. You can read up on what various facial expressions may signify. [1]
If you're not trained and experienced in this sort of thing, with positive results, I would strongly advise against trying to make decisions in a job interview based on what directions you think the interviewer's eyes moved.
I could see that. I guess a better way to say it is just to pay attention to their overall body language.
I've actually never had a skip-level one-on-one. What do you think you get the most out of them?
It is a test of the level of trust of managers in a company. If you are working for a micromanager or a lesser experienced manager, they would never imagine you talking to their boss, ever. If anything they might even threaten to fire you if you "go above them".
I could see that. I think there should be routine talking up and down the chain of command. I once worked at a place where most people actually kind of feared talking to a VP. I always thought it was very strange.