Factual error: Jack enters the tournament as a recognized white belt but he is scheduled to face Kim who is ranked as a black belt. Tournaments do not allow match ups between white and black belts; it's forbidden in all styles of martial arts.
Factual error: It says that Jerry is running a judo dojo, but when Jack walks in Jerry is teaching his students to punch - judo doesn't use punches.
Answer: It depends. If you watch the action scenes in slow motion, you can often tell if it's the actor or a stunt double. Leo Howard seems to do a lot of his own fight scenes and acrobatics while many of the fights and flips by other characters are done by doubles; although occasionally Olivia Holt will perform a simple flip or fight.
Both Leo Howard and Olivia Holt have black belts and completed their own stunts.