I wanted to ask if he knows about Login with Lightning and if not, show him how I log into my SN account and explaining the simple protocol.

If he says yes, I will just ask what his opinion is on it. I assume he will explain how it works then to point out flaws or advantages.

I will think about a way to proof that I am not lying about the outcome.

Maybe taking a picture of two different hands of a letter on which is written "Yes, I knew about LNURL-auth" or "No, I didn't know about LNURL-auth" with a slide of the lecture in the background?

Should be private. Maybe I can also ask him how I can proof it in a private way since I think he also works on privacy stuff haha