Contrary to what its name and look implies it is not a turtle, but a dragon by Guild Wars game mechanics.
A large group of Bonesnap Turtles can be found due north of Zen Daijun, along the coastal cliffs. This is the most ideal location for farming Bonesnap Shells for the Canthan New Year festival.
Once a player has completed Winds of Change part 2, the Bonesnap Turtles will be replaced by much stronger Scavengers. This can be avoided by bringing someone who has not yet completed Winds of Change.