[Can't find Skill Mentor at Republic Fleet?]

Republic Fleet, Carrick Station, Combat Training Sector, -4755,694 (bottom room just left of vertical centerline of map). Name is Leuro-Khian.

[Skill tree reset]

For a more specific answer for Republic, the Skill Mentor is at -4755, 694 in the Republic Fleet. (Bottom room left of center on Carrick Station Map). His/her name is Leuro-Khian and doesn't show up on any icon on the map. When you mouse over the NPC, your cursor changes to conversation bubble.