Oketra's first triggered ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered.

In the Commander format, a commander's color identity isn't affected by color words (such as black) appearing in its text. If God-Eternal Oketra is your commander, your deck can't contain black mana symbols.

If one of these Gods leaves the graveyard or exile while its last ability is on the stack, it will remain in its new zone, even if that zone is a graveyard or exile.

If the God's owner has two or fewer cards in their library, the God is put on the bottom of their library as its last ability resolves.

If you control another player's God when it dies, you decide whether to put that card into its owner's library.

If an effect exiles the God and immediately returns it to the battlefield, its last ability triggers but will have no effect. However, if an effect exiles it and would return it to the battlefield at a later time, the God's ability may return that card to its owner's library first. If it does, the effect that exiled it won't return it later.

In a multiplayer game, if you put another player's God onto the battlefield under your control, it will be exiled as you leave the game. If you were still the controller of that God, you would control its triggered ability but you have left the game; that ability won't resolve and the card remains in exile. Similarly, if you lose the game at the same time that another player's God that you put onto the battlefield is destroyed, it remains in its owner's graveyard.

If one of these Gods dies and it's your commander, you may put it into the command zone before its ability puts it into your library. If you save your commander this way, it won't put it into your library. The same is true if it would be exiled.