So I just recently started seeing this on the forum [I only joined a month ago] and I'm wondering where people found evidence of Vivecs trial, from Oblivion? From Skyrim? Where is all this info coming from

It was a roleplay on this forum from after Morrowind. The threads are backed up http://imperial-library.info/content/forum-archives, and you can read a summary http://www.imperial-library.info/content/trial-vivec. I strongly recommend the threads, though, the way the conclusion plays out it awesome.

There was supposed to be an indirect mention of it in the Pocket Guide that shipped with Oblivion, but it was cut due to space. You can still read that content http://imperial-library.info/content/imperial-census-daedra-lords. And of course we know that Vivec disappeared under mysterious circumstances after Morrowind. I doubt it will officially ever be confirmed/denied, just like the fate of all the game's player characters.

It came from a roleplay/discussion that many of the big names in Lore writing (not the least of which Michael Kirkbride) took part in. As it hasn't appeared in-game, it's status as canon is disputed.

EDIT: Ninja'd. Curse you Lady Nerevar!

The Trial of Vivec. Shining moment of awesome for Vivec, pretty much.