Well here is what I remember doing, I can remember when we were talking about winter sports and the like I asked her "so are you a snowboarding fan" (even though I had previously known that), then when I was talking about the city where me and the rest of my family used to accompany my dad when he had conferences there I said something along the lines of "something tells me you know a lot about that city" and then she told me that she did indeed grow up there. It's all about trying to slide it in without being too obvious.