How many alternate Superman are there?

Answer 1

difficult to answer, because of the way DC multiverse is structured. If you accept that there are 52 universes in DC continuity, then there's one iteration of him in each of those universes. However, there have been many tales of alternate past and future supermen, under the "Elseworlds" imprint. You should also take a look at "Hypertime", a recent innovation in DC comics that basically allows the multiverse to constantly re-write its own continuity. It all suggests that there's an infinite number of Supermen. It's subject to interpretation.