This is an unusual interview for Actors Talk August: a duo of young actors just finishing their first August Wilson play. Brenden Peifer and Melessie Clark are playing Sterling and Risa in “Two Trains Running,” directed by Justin Emeka at Pittsburgh Public Theater (through June 19). Their first encounter with August Wilson traditions, characters and an experienced cast feeds plenty of thought by two lively, smart, responsive professionals just starting their August Wilson journeys.