Does activating Priest of the Forgotten Gods ability trigger Korvold's last ability twice?
Yes, activating Priest of the Forgotten Gods' ability and sacrificing two creatures simultaneously triggers Korvold's last ability twice.
Rule 603.2c says this:

603.2c An ability triggers only once each time its trigger event occurs. However, it can trigger repeatedly if one event contains multiple occurrences.
Example: A permanent has an ability whose trigger condition reads, “Whenever a land is put into a graveyard from the battlefield, . . . .” If someone casts a spell that destroys all lands, the ability will trigger once for each land put into the graveyard during the spell’s resolution.

In this case, the single event of activating Priest of the Forgotten Gods contains two occurrences of sacrificing a creature, so Korvold's ability that triggers &quot;Whenever you sacrifice a permanent&quot; triggers twice.