Learn somebody's mother's maiden name.

I learned my boss's mothers maiden name by asking what her middle name was and then asking whether that was her mothers maiden name or a given middle name. It turns out that I got lucky and that was her mother's maiden name and not her given middle name or her own previous middle name. Sounds a little complicated, but basically I got lucky that I didn't have to awkwardly ask more about her cultural heritage or something to get more info about her mothers background and therefore maiden name.