Luca will teach you how to focus. He teaches the Focusing Skills, which allows you to learn a variety of useful Skills. Luca also teaches the Brawling Skill, which improves your unarmed combat. It isn't very effective currently but might be improved later.

He is located est from the Soul Menhir in Tulimshar, just follow follow the dirt path to the east. You'll pass by Elanore, then Cyndala. When the path forks, travel north a short distance. Luca is on your right, standing on a cobblestone square surrounded by blue warrior banners.

You can find the script here.