Visible crew/equipment: When Kim is talking to Joan the security guard, a crew member drinking a cup of coffee can be seen in the dojo.
Gold Diggers - S4-E2
Visible crew/equipment: At the end of the episode when Milton is talking to Jack, a tube is seen next to his legs for the dust to come out. (00:36:00)
Visible crew/equipment: During the race, cameras can be seen on Kim's helmet.
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.