OJ command and ajani's pridemate

[Jamie]

I return ajani's pridemate with ojutai's command from the graveyard and gain four life.
Does the creature trigger?

[hamfactorial]

Yes. Both modes of Ojutai's Command resolve simultaneously, so Ajani's Pridemate is placed on the battlefield at the same time that you gain 4 life. Since the Pridemate sees you gain the life, its ability triggers.