Does Trunks know how to fire a Kamehameha? I was watching this segment from a non canon movie (which is known to have some animation mistakes such as Krilin's "Super Saiyan" aura) and Trunks seems to do the pose, and he says the words like someone firing a Kamehameha.

I was wondering if his  Kamehameha scream was something made up by the dub, or if it was in the original Japanese audio, and in the case Trunks was genuinely made to fire a Kamehameha in the movie, if this is congruent with the series or does just Trunks supposedly know how to fire a Kamehameha only in the non canon universe?
Trunks has never fired a Kamehameha in any of the canon versions of the series. He does use the attack in GT and also in the case of the movie as you stated. Essentially, the attacks used by the Hybrid Saiyans are generally based on the attacks used by their respective fathers. Which in Trunks' case, is the Galick Gun and Final Flash and Kamehameha in case of the Son Family. I wouldn't necessarily say Trunks' scream was made up by the dub with regard to the movie as you can see  here.