if you are asked the question "tell me something i don't know " what answer would you give

You could say, 'Well, you just heard me.' 'Tell me something I don't know,' when used colloquially, is not a question per se. It is often a rejoinder to a trite comment. You probably have said something commonplace, and your hearer says, 'Oh, yeah? Tell me something I don't know.' And you don't begin to feed him the news. You just find a quip, like the one above: 'Well, you just heard me,' or something else of the sort.

Peace out!

@kuwena
That is a good one, but what if no previous statement of that sort was made?

That could equally be a question depending on the circumstances it was asked anyway. It could also mean asking you to lay emphases on what makes you different from others or what is that thing (experiences, skills, achievements, etc) we don't know that will make us hire you instead of the others.

In such case, take your time to tell them your skills or achievements, or anything that will make you stand out.

More opinions are welcome on this.

Thanks and One Love!!!