Where Second Godzilla from Godzilla Raid Again got expose at?

Probably the same island. It's likely the second one fled to the ocean to feed and recover it's strength after it's long hibernation.

For all we know, both Godzillas could have been active during the events of the first film. The second Godzilla was confirmed to exist only months after the first's death, meaning that they could have both been attacking ships in the Pacific at the same time.

Well, to me i believe that is where dr. yamana's warning came into play. "I can't believe godzilla was the only surviving member of it's species.......but, if we keep on conducting nuclear tests, then another godzilla might appear in the world, again" I believe that the second godzilla was hiding it out.

Or i probably agree with the king of the monsters.