This page of the Assassin's Creed Valhalla Dawn of Ragnarok game guide contains the location of all the abilities available in the Gullnamar region.
Location: This ability is hidden in a small building located in the southern part of the region.
To get to the book, you must first solve one puzzle. Start by moving the last (or first, when approaching from the outside) ray. It must be directed towards a point on the left column. This will allow light to penetrate further.
Your next move should be to destroy the wooden crates lying next to the next beam. Note that there's a ball lying on the crate. You need it. You must pick it up and place it in the last projector.
After placing the sphere, direct the beam of light to the point above the door. This will open it up and allow you to go inside and pick up a new ability.
Location: You will find this ability in a cave, in Uldar.
To get there, you must start by activating the Power of Muselheim, which will allow you to safely walk on lava.
Your task is to direct the beam to the element above the door. The beam will distribute the beams so that a side door will open. Behind them is a small room where the book is hidden.
Location: You will find this ability in a building in Uldar.
Your task is to position the rays so that they open a closed passage. To do this, first point the beam at the projector inside the building. It should be positioned so that its beam reaches a point above the door on the left.
Remember, there's a beam of light coming through that door. Just drive up through the open window and you'll get inside. A skill book is hidden behind an open door.