Knowledge through quest : "ABOUT THE CRIMSON DRAGON GARMOTH"
Start NPC Odelphin in Duvencrune ; 5x Garmoth's Scale needed

Disculpen solo esta esa misión?? no hay manera de poder sacar la S? si es que no te la da al completar la misión

In order to acquire this knowledge you need to complete a quest:https://bdocodex.com/pt/quest/7225/1/?sl=1 , the scale that you need, are, most of the times, available at marketplace for a total of less than 5 million gold.
Keep in mind that you can actually get this knowledge only ONCE PER ACCOUNT!!! So please use everything you can in order to achieve higher rank grade (elixir/pet/event bonusses...)! If somehow you get a low grade, well you are not alone sadly.In order to change this system i made a feedback on the official forum , you can got there and support the feedback by adding one upvote , and maybe one day PA will allow us to "reroll" this knowledge.

NB:this is the case for some knowledges and i extend the feedback as soon as i discover another knowledge in that case; already made a ticket for that and the GM just told me to go to feedback section. If in any case you deleted the knowledge, try to ask for a new one in a ticket as its your sole solution(which i can't guarantee).
Why getting high grade is important: Decreased damage received when the target hit you; Deal extra damage to the target (which can be interessting in order to achieve DPS rank against world bosses);Extra drop rate (even if it may or may not work against world bosses);Ecology point system;personal completion.

Ok I haven't tried yet... but am I wrong in assuming that you CAN farm Garmoth for S knowledge doing The Last Ritual quest in the Drieghan questline? Like keep forfeiting the quest once you've beat him until he gives you S?

As far as I know usually you CAN get boss knowledges in the character quests where you have to beat a boss. I have two chars that have completed this questline but i'm gonna try in the next few days with an alt and see if that works.

Killing Garmoth in the Mainquest dont give knowledge.

Our prayers have been answered. From today april 9th 2024 patch:

"Added new means to learn the Garmoth Knowledge for those who've yet to learn or deleted said Knowledge.
Improved so you can now acquire the Garmoth Knowledge from looting Garmoth after defeating the world boss herself.
Adventurers who've already possessed Knowledge of Garmoth will not gain additional Knowledge from looting this item off Garmoth, nor will it increase its Knowledge grade."


This means then (I Imagine?) that if you keep deleting the Garmoth knowledge and beating her again you will eventually be able to get S knowledge, don't know why they just didn't make this some npc you need to talk to like all bosses but it's better than nothing. That leaves only mutant troll and ogre as knowledges that are nigh impossible to get at S unless you were super lucky with those one time quests. Our only option there is still to SOMEHOW find a group to do the boss that will let use give that last hit. If they changed their mind on Gsrmoth though we can hope this will come eventually.