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/jp/quest/2001/50/)
Note I've not done this knowledge myself, but I belive its gained from interacting with smth along the mission.
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.
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Anonymous 23-08-2017 19:32
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!!