I’m an alien. No, really. I’m from an high-advanced civilization. But you don’t believe me. So you ask for a demonstration.
Among other things, you ask me to share a scientific knowledge totally out of your league but that you could be able to verify in a few days. Something that makes scientists says "Ok, it's not one of us."
I will give you only something completely innocuous (physically and socially) and that will not lead to great shock among the public. Maybe something that’s just a matter of interest for the scientists.
So... what could I give you?