You need:
Remnants of the Rift
https://bdocodex.com/id/item/43786/?sl=1

to get:

You need "Remnants of the Rift" in your inventory.
- Right click at the item, it's going to navigate you to NPC Martha Kiyen, then you can start the questchain. (Blackstar)
- You can choose any Blackstar gear to proceed with the quest, I chose sub-weapon one >>> https://bdocodex.com/id/quest/3441/31/
- This quest will send you travelling back and forth between Star's End and North Calphaeon.
- Keep doing the questline until it navigates you to find Caphras Research Journal in the cave next to Florin.
- You go to the marked location inside the cave where the quest navigates you to find Caphras Research Journal.
- You need to walk up the short stair on the right side, then look for the last bookshelf on your left handside. (It's name is Caphras Research Journal.)
- Interact with that bookshelf, then you will get this knowledge.

From now on you can stop the questline. But if you keep doing it , you will get another knowledge for Star's End Adventure Log III, which is optional.