Mother Giselle Not triggering Dorians first quest

One way to determine if she's not giving you the quest is to see the Dorian cutscene where he talks about Alexus.  After that cutscene, an exclaimation point immediately appears in Skyhold where Mother Giselle appears in Skyhold.  If she does not offer that quest after that cutscene, the game is bugged.

Sorry, I meant Felix Alexius

Not the judgement scene, a cutscene with Dorian in the library discussing Felix (how he was Dorian's only real close friend in Tevinter, etc etc).

I have heard that doing the Gereon Alexis judgement and talking to Dorian about it afterward bugs the game.  Try to avoid judging Alexius in an earlier save and try and get the Felix cutscene.