So I solved the portal puzzle and made it to the library. I picked a skillbook and the other two disappeared. I found a note in a chest with a riddle referring to a specific digit. There is a lever next to the portal, not sure what it does. I guess it allows you to go back and forth between the library and entrance portals.
I can't find anything else in the library or previous room. Any idea?
You've found everything of value there. Case closed.
