Sasuke asked me, "Papa, 何 doing?"  I showed him how to put the gas in, and when he was much farther away, how to start it.

"Nani doing?" has become a catch phrase lately.  It's also interesting.  He combined the easiest parts to say from "nani shiteru?" and "what are you doing" which mean the same thing.  He has trouble with 'S' sounds, and "nani" is much shorter than "what are you." Hence, "何 doing?"