You get it from:
Balker Batian
You need this Quest:
Goodwife of the Batians
Or you have to be higher as level 36.
If you are higher as 36 or you did made the Quest you can start with this:
Power of Women

@Admin: Balker Batian have nothing to do with this...the Game say "from a Quest from Balker Batian", but I could got this in a early stage.
http://bdocodex.com/de/quest/3101/1/?sl=1
This Quest did I made and then I got the knowledge.


Edit: I got it from this Guy:

On Calpheon, Outside the store of Lavientia Batian, Accept the quest from the villager : A Sinner
Talk to one of the priest in front of him. You will get the knowledge.

The quest giver for {A Sinner} is outside the church in the upper part of Calpheon. The man is in the crowd with his arms crossed. then talk to the High-ranking priest to gain the Knowledge of Road of Penitence.