The Ram's Head Thogchag is the fifty-second treasure that can be found in Uncharted 2: Among Thieves.
The Ram's Head Thogchag is found in Chapter 16 - Where Am I?. As soon as you gain control after the cutscene, you can find the very first of three treasures found here. Leave Tenzin's house, and turn right, and then right at the black and white yak cow, you'll reach the back end of the house. Keep an eye out for the treasure's glimmer on the ground next to some tables.