The Carved Bone Ornament is the eighty-eighth treasure that can be found in Uncharted 2: Among Thieves.
The Carved Bone Ornament is found in Chapter 23 - Reunion. there will be a zip line just after the puzzle with the shapes and Tibetan letter. Just after the zip line action, you will jump over a ledge where there will be a set of wooden stairs. Walk up to the gap in the stairs and look directly up and slightly behind you. Shoot it down to collect it.