Hope okay to share: One of my exercises I learned years ago which still sticks with me... is looking through a photo album with your character when he/she is old, and ask about a particular photo from when they're young(er) -- let him/her tell you about that person/situation. A couple other things that aren't really interviews but which reveal a lot nonetheless --- imagine your character stuck in line somewhere -- at a store, to some event, whatever. Spy on them to see how they act, if they're cordial, if they "cut in", whatever. Another is seeing what they have in their pockets or in their purse. Sometimes it's the smallest nugget of information or of personality/behavior that sparks necessary knowledge of that character.

JoniB22, I like that photo example. Good one. Re stuck in line? Concur, small habits can reveal larger truths about characters. I came up with one the other day: Does the character return their grocery cart to the collection unit or do they leave it out in the open in the parking lot? Again, a tiny thing, but reflective of a personality trait. Thanks for the suggestions!