Currently the knowledge entry of Magic Crystal of Infinity - Descent is impossible to obtain.
The alchemy recipe to create it requires "Magic Crystal of Nature - Descent" which doesn't exist in NA/EU version of the game and there is no hunting monster that drops the "Magic Crystal of Infinity - Descent" either which would give the knowledge entry.
I suggest a simple fix to this issue would be to add a dialogue option to the NPC "Dalishain" just like the "Magic Crystal of Infinity - Experience" was.