The Tibetan Prayer Wheel is the forty-ninth treasure that can be found in Uncharted 2: Among Thieves.
The Tibetan Prayer Wheel is found in Chapter 15 - Train Wrecked. It is advisable to wait until all are cleared before searching for it. To find this treasure, head far left from where you started and follow the cliff wall. You will see the treasure flashing on the ground. You want to follow the cliff past the train cart that is suspended by other debris. (this wreck should be on your right side).