You need to get the beginning quest from Chief Florin (Valentine). Name of quest is called : [Alchemy] Secret Duty. Follow through everything till [Alchemy] In Search of Caphras' Journal.
None of this helps like every time I go to an Nov they have nothing for me bdo codex is a joke doesn’t say shit or even tell you who to even go to tuck this page.
As the first comment and "Obtained from" says, you can get this knowledge while doing the In Search of Caphras' Journal quest by interacting with certain object. Check the comments and screenshots on the quest's page for the exact location.
Get the quest secret duty from valentine the florin node manager. https://bdocodex.com/tw/quest/3042/1/
complete the questline to obtain the knowledge.
you only need in search of caphras journal