Questioning Beliefs is a companion quest for Fenris in Dragon Age II Act 2.
Acquisition
The quest becomes available at 50% friendship or rivalry.
Walkthrough
Fenris tells the story of his escape from Danarius. Listening to his story and choosing diplomatic responses nets
Fenris: friendship (+15).
Note: If Hawke is planning on romancing Fenris this quest seems to be a necessary prerequisite for that. The romantic options following Fenris' story seem to be what instigates the romance relationship. (The conversation here is what grants the Flirtatious achievement, not the follow-up in A Bitter Pill.)