It's almost impossible to tell where the pipe is without some expensive equipment. I would investigate the door before looking for a broken waste pipe. Generally speaking, waste lines aren't run horizontally through a slab if it can be avoided. Whenever a waste line goes through concrete, it's always wrapped with foam to allow some movement . That makes me think it's the door leaking. Pull up the damaged floor and have a look. The floor is toast regardless, so you have nothing to lose by looking.