Unrelenting Grip is a skill located in the Ardent Flame (which can be found in the Dragonknight skill tree). Unrelenting Grip is a morph of Fiery Grip.
Unrelenting Grip deals the following types of damage: Flame Damage. Which means that it gets buffed by the following blue champion point trees: Elemental Expert, Elf Born, Master at Arms, Spell Erosion. Also the following red champion point trees protect against this skill: Elemental Defender, Iron Clad.
ESO Skillbook