Can be obtained from the 300 animity quest from Isobell in Heidel. Requierments for the quest to be accepted are as follows: 2 pre. quests done, 10 to 12 pm, raining. (http://bdocodex.com/cn/quest/2001/50/)

Note I've not done this knowledge myself, but I belive its gained from interacting with smth along the mission.

wont work for me look screen http://i.imgur.com/5RDVoPQ.jpg
No quest for me

You can find the knowledge inside Heidel Castle, be careful as the mobs there can 1 shot you even at lv50. You need to stay out of their line of sight. The knowledge is in a little room on a balcony right at the back on the screenshot.

ALERTA!! o castelo de heidel é zona de ataque, resumindo entro la os npc mata!!! entao larga na pernada,que na sala do trono nao tem npc pra ti mata!!