"Check the gate" means to look at the lens of the camera after a good take, to make sure there's no hair or dust in it. If the gate is clean, the take is good and can be printed, and the production moves on. At the end of a take the director likes, they yell, "Cut! Check the gate! Print it! Moving on!" Stuff like that.
I mentioned it to my Lyft driver last night and he said, "Yeah, man, what is it about being in power that ALL these people do this sick stuff??" Total normie, but woke af.