Yes anyone driving a Jet Ski or Riding on a Jet Ski must wear a Life Jacket when on that Jet Ski out in the water.
The life jacket must also be worn by anyone being towed behind the Jet Ski or any other watercraft.
The Life Jacket must be Coast Guard approved and be worn by everyone on board the Jet Ski.
Even if it were not the law it's still a very good idea to wear a life jacket on the Jet Ski to save your life or your passengers life should an accident happen.