I just finished checking all Puzzling site tags. I recall a tag that meant that the puzzle involved knowledge about the site itself, and maybe a user, but I didn't see it. Was it deleted? Did I not notice it?
We at least don't have such a tag right now. (Speaking as someone who's read through all our tags repeatedly). However, knowledge works for any sort of specific knowledge required.
I would urge you to be careful when referencing specific users. Please, please get permission first. Also, be aware that users change. Activity goes up and down, profile pictures and "About Me"s are edited, puzzles are posted and deleted, etc. See this meta answer