Currently with the revamp of the missions you have to do until serendia II to release the knowledge, when you finish the missions just get the black spirit

November,23,2025

After spending a whole weekend hunting this knowledge, i can safely say.
You need to do:
Serendia Questline
Calpheon Questline
[Witch Story] The Returned Pendant

after you complete the [Witch Story] The Returned Pendant questline , the Black Spirit will have 3 different knowledges to get:
-Reasons for Rebelling-
-Travels in Mediah-
-The Only Thing that Matters-
thats the 3 that appeared...

getting this knowledge is a slight pain.. but keep it up!