These are required levels for crafting Witcher gear items.
It turns out the Grandmaster Wolven Gear diagrams are kept in two sets of three. Both quite close to each other, hidden in Termes Palace.
The extended Yrden circle is 40% bigger than normal, it replenishes Geralt’s stamina quicker when he’s inside it, it lowers his damage taken, and doubles Geralt’s Sign intensity.
I find Isabelle Duchamp’s journal and it points me in the direction of the first Grandmaster Wolven Gear crafting diagram.