Could you suggest a good survey paper on positive mass theorem?
H. Bray's articles "Black Holes, Geometric Flows, and the Penrose Inequality in General Relativity" (Notices AMS, 2002) contains a very short, but elegant, survey of the positive mass theorem. He also has a longer survey that goes into several simpler cases.
Maybe Markus Khuri's RTG notes would help?
There's also a set of lecture notes by Rick Schoen for his 2009 course in Stanford on General Relativity, which has a nice discussion of the fundamental ideas involved in the proof of the PMT. I don't know if it is publich available on the internet though...
Lecture notes (2009) by Rick Schoen on Relativity :