Sure... but then it might make them uncomfortable if they can't think of one. I don't think there is a full-proof system for this, and it's not even a bad thing, maybe it's meant to be that some people have common interests in some aspects and different in others.
Perhaps another thing to try would be to ask them to tell you a joke ?
(I'm a bad example though, I don't remember/collect/write them.. a mere consumer.)
Sure... but then it might make them uncomfortable if they can't think of one. I don't think there is a full-proof system for this, and it's not even a bad thing, maybe it's meant to be that some people have common interests in some aspects and different in others.