"Truth"

 
Part of the definition of being a Knight is that he commits to "openly and honestly communicating with her on all aspects of this lifestyle."

Doing this requires him to open up and to thoughtfully consider what he says. This is a very different mode of answering than normal conversation.

This Wish makes clear to him that she wants a full and honest answer to her question(s) so rather than answering casually he will answer as her Knight.

This Wish can also be used when Telling Others about Devotional Sex as the Wish tells him that he has permission to and/or she really wants him to give a full and open answer.