The quest becomes available at 100% friendship or rivalry.
- If you have completed Isabela's Regret, the cutscene begins with Isabela offering to let Fenris sail with her, Fenris simply comments that she doesn't own a ship.
- If Isabela is gone, or her companion quest hasn't been completed, it begins with Varric and Aveline speaking with Fenris about his house.
If in a rivalry, Fenris will instead be pacing restlessly in front of the fireplace. He will be angry over how his revenge "tastes like ashes", but he will then calm down and ask Hawke what he should do now that he's free.
If in a friendship, Fenris will say his freedom doesn't feel like it should, even though Danarius is dead. Peaceful/Sarcastic/Aggressive responses all lead to Fenris suggesting it might be time to move forward and asking where Hawke may think that leads... The 2nd Sarcastic response warrants a chuckle from him, the 2nd aggressive response causes him to check his attitude, but all end the same. Choosing "I don't care." about what Fenris' future holds will result in him saying "I had hoped you might..." showing his desire to have been a friend to you, but this doesn't affect anything. Choosing any other response will result in him commenting on being a firm friend until the end.
If Hawke was in a romance with Fenris in Act 2, then Fenris will bring up the fact that they "had not talked about what happened between them three years ago." At this point, you will be able to question his reasons for leaving and choose whether to rekindle the relationship, or cut it off permanently. If Hawke slept with someone else after Fenris left, he will bring this up.
Fenris can leave the party permanently at this point if you choose the option "You should leave". He will thank Hawke and state that he will go west.
If this quest is completed, Fenris will subsequently support Hawke during the climax of the story no matter what. If the quest is not completed, Fenris will initially refuse to go against his principles.
If you've needed to use the console to make Isabela romance you to fix the bug in Demands of The Qun, this may have set the 'Denied' or 'Ended' flag on the romance with Fenris. You will need to use the console to clear those romance flags before Questioning Beliefs will progress correctly for an Act 3 Fenris romance. You may also need to set the 'Active' flag on Fenris' romance.