Questioning Beliefs is an Act 3 companion quest for Fenris in Dragon Age II.
Acquisition
The quest becomes available at 100% friendship or rivalry.
Walkthrough
The cutscene when Hawke speaks to Fenris seems to be different depending on whether the player has completed Isabela's Regret.
If you have completed Isabela's Regret, the cutscene begins with Isabela offering to sail with her, Fenris simply comments that she doesn't own one.
If Isabela is gone, or her companion quest hasn't been completed, it begins with Varric and Aveline speaking with Fenris about his house.
(1.04) This does not seem to be the case if the player is in a romance with Isabela and has completed Isabela's Regret, but there has been other ports that Isabela's cutscene plays regardless.[confirmation needed] If Hawke was in a romance with Fenris in Act 2, then he 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 up this topic.
Fenris can leave party permanently at this point if you choose the option "You should leave". He will thank Hawke and state that he will go west.
Result
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.