The Yuan Dynasty Lotus Jar is the fortieth treasure that can be found in Uncharted 2: Among Thieves.
The Yuan Dynasty Lotus Jar is found in Chapter 12 - A Train to Catch. Before you make that jump from the fire escape to your right, however, why not grab yet another treasure? That's right, the first two treasures (of five total) in this chapter are located this near each other, and this near the outset of the chapter. To get this one, it's simple. Once you're on the fire escape, don't follow Elena's lead and jump to your right. Instead, seek out a staircase that leads up to a higher tier of fire escape, directly above you. If you scour this fire escape, you'll easily find the treasure you seek.