The Golden Seadragon Pendant is the fifty-eighth treasure that can be found in Uncharted: Drake's Fortune.
The Golden Seadragon Pendant is found in Chapter 19 - Unwelcome Guests. This badass treasure can be found in the area where you fight all the guards and the Descendants at the same time around the large wooden boxes. Climb on top of the pile of five boxes against the back wall, then jump over to the nearest pile of two boxes, and then finally jump to another pile of two boxes against the back wall to claim this seadragon.
A simpler way to do this is to climb up the side of the boxes that the treasure is on.