As far as I know...two handed tapping would be like hammering on some notes with both hands consecutively. For instance...u could play a chromatic type thing so one hand would play like 5,6,7,8 on the high e string and ur other hand could play 9,10,11,12 right after that. Thus using all 4 four fingers on both hands. Jennifer Batten did a crazy two handed tapping version of Nicolai Rimsky-Korsakov's Flight of the bumblebee utilizing two handed tapping in this chromatic fashion. That's what I've always thought two handed tapping was. Hope that helps.