[Finn's been around Jonathan long enough that any initial weirdness has passed regarding the combination of human and Argonian features.]

He knows I grew up in a small fishing village in Morrowind, spent a year in Skyrim before I got ported in, had an embarrassing incident when I was still a novice alchemist.

[He knows what Lucien's referring to, he just likes keeping things light.]

He knows I killed Grelod the Kind and that I did it to save the children she was abusing, but he doesn't know about Aventus or what happened afterwards.