Peng's treasure is a small, hidden collectible in Dead Space 3 that takes the form of a small statue of a woman. It can be found in the Reaper Barrack's optional mission, late in the game. As you progress through the mission, you'll come accross some big pulverizing machinery. In order to make it past the machinery, you need to use your stasis module. Once you've made it past the machine into a central space (just before another masher), turn around and hit the machine with your stasis again. You can't move into the corridor the masher occupies, but you can look past its large steel bars and behind where the machine comes to a rest. There, you'll find Peng. Use your Kinesis module to pick it up and then it A or X to collect it.
If you still need help, here's a youtube video showing the location (nevermind that it's in German):