Obtained from a corpse in Stormveil Castle, on top of a watchtower. From Rampart Tower Site of Grace, head through the southern door, hang a right, and climb the spiral staircase. Enter the outer hallway, and circle around to the exit that leads to a rooftop. Use the pile of sandbags to climb onto the wall, use it to reach the ledge of the attached tower, and jump over to a nearby tower, whose crown has been destroyed. Drop down into this tower, and then down onto a roof, next to a Warhawk. Head across a small connecting rooftop to the next building over, where a broken pillar lies leaning against a wall. Climb up this pillar, sneak around a ledge, and climb a ladder to reach the corpse.
To put these numbers into perspective, the most common motion values of that specific attack input for Curved Greatswords are +27%, while the most common MVs for Claws are +22%.
Note that while several skills may make it look like the character is jumping, such as Skill: Lion's Claw and Skill: Loretta's Slash, the only skill that can actually directly benefit from this talisman is Skill: Raptor of the Mists, as any attack performed during jump that happens when the skill is used to avoid an attack is considered to be a jumping attack.
Patch 1.09: Decreased the effectiveness of the Claw Talisman.
This is the patch that decreased the boost against other players from 15% to 7.5%.
Patch 1.05: Fixed a bug where the “Claw Talisman” effect was not applied when jumping with the "Starscourge Greatsword" in both hands.
The bug was that the Starscourge Greatsword's jumping light attack did not have its damage increased when the talisman was worn if the weapons was two-handed/held in each hand (since it's a paired weapon).