So, just like, full questions?
Trying to think generally here... those questions that really get beneath the skin tend to do with personal stuff! I think you'll find that once the players get underway doing their thing, a lot of interesting stuff will pop into your head. A lot of things will go unanswered! But here's some stuff on the top of my head:
How did you get your (whatever item)?
Where do you live? Draw it on the map, here. What's on your walls? Where did you get your furniture from?
Who do you work for? What do you do to get barter?
What's the maelstrom like for you? How long has it been since you last used it? What do you think it is?
Which (of the other PCs) would you save, if you could only save one? Why?
Just remember: barf apocalyptica on it, bring it back up in play. Start with general stuff, "How do you do this, where do you find that," then slide the spectrum towards more personal stuff, when those personal details actually emerge in play. Wait for their characters to react to someone or something, then ask why.
But okay, more questions:
Do you eat the food from the creek, or wait for the traders to come in? Why? (obviously change the details to suit what you've come up with, the main idea being: present them with choices, and see who picks what, and what does that say about them?)
Have you two (players) ever gotten in a fight? (I personally love to start shit with my questions. Love, love, love it.)
Who would you turn to in a real emergency?
Where do you see yourself in five years?
I don't know if you've ever stolen anything from these guys, but if you had to pick, who's the easiest to steal from?
You'll find the kinds of details you want when your questions ask about or imply bits of the world, or personalities.
If you want them to fill in the world more, easy. Pick a place on the map, and just ask about their experiences there.
Who's been to the Hole here, and what's it like?
Have you bought slaves from Abondo? Everyone says he steals them from the camps on the coast. Do you think that's true?
Every now and then, throw in one of these. This is up to preference, of course - these questions give the power directly to the player, and some MCs might not like that:
What the fuck is THIS thing, over here? (pointing to something on the map).
Why is Rock Town abandoned?
But absolutely bring up any setting element they name drop and ask about it over and over. Get different players' opinions on the same area or person.
YOU: "Where do you get your ammo from?"
THEM: "Uhh... who sells that kind of thing here?"
YOU: "Let's say Isle and Mimi. They're the big weapons dealers. Nobody else really has enough to be worth your time."
THEM: "Okay, let's say Isle."
YOU: "Why Isle, why not Mimi?"
THEM: "I don't know, uh..."
YOU: "Just make it up!"
THEM: "Isle's cheaper?"
As soon as you find someone who buys from Mimi instead of Isle, ask why, why, why.
And think off-screen - why is Isle cheaper? Is she really cheaper, or is she giving that player a special discount? Shit like that goes on your sheet under I Wonder.