I always fill these with awkward or absurd questions/anwers that would be amusing if a human operator ever needs to verify them. E.g.
Would you like to go on a date with me?
What color pants am I wearing?
What is the square root of insanity?
Obviously you need to store these in a password database in order to remember them, which kind of defeats the purpose. If I have to choose from predefined questions, it goes along these lines.
Q: What was your mothers maiden name?
A: Why, are you stalking her?
Q: Where were you born?
A: Oh I can't remember, it's been so long!