Can be found by examining the four statues on top of the Wizards Altar

jo hier ma genauer etwas

10 energy is needed for this

To expand on the comments above... it's on the wizard altar where you upgrade your black spirit, climb up the tower like your going to the black dragon and there is a Ladder on the north side of the platform you can climb behind the dragon. There will be a smaller dragon you can interact with but it's not the correct one, climb on over him and make your way around the left side of the tower... you'll see a small platform you can walk around on and the dragon with knowledge is there.

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