I'll be upfront right now and say I hadn't looked into the application process for being a mod and what you might have already put forward to get your 16 canadits, but I did have some general ideas because I've run mod-selection for a group I was a mod for before I left that site.

Some of the things we've done were a lot of hypotheticals. Like:

A user is being confrontational with you over (insert reason.) How would you handle the situation: A) if it is being done in public, B) if it is being done via PM/DM? 

A user has raised a complaint about another user over (insert reason.) What do you believe the proper course of action should be?

([@Hyde] already nailed the "previous experience" question. lol.) 
But, to build on that, perhaps just a more generalized: Do you have any experience in de-escalating arguments/problems, or enforcing rules/policies? 
(It's complicated to address this question, but people that have experience working as customer service reps, or management positions, or even as parents and teachers would have experience there that they may not attribute to having been a modorator elsewhere.)