Looking through Dracovish's current movepool, I can only think that it learned Psychic Fangs. In which case, I think it'll be the one to ultimately defeat Dragapult.
As for the other matches we're shown, given that Ash is switching his team around, I think Sirfetch'd and Mr. Rime may draw, Ash will send in Dragonite against Dragapult, only to switch to Lucario. And when that doesn't work, he resorts to Dracovish, who'll beat probably beat Dragapult. After that, anything goes. But that's just what I'm hoping for. I really don't wanna see Dragonite lose again.