Inside a brightly lit office in Shanghai, Kim’s task for the week was to pretend he was opening the door of a microwave. Wearing a virtual reality headset and exoskeletons on his arms, he repeated the movement hundreds of times a day so that the humanoid robot next to him could learn it. On other days, Kim mimics folding clothes, or stacking wooden blocks. Kim, a 20-year-old computer science major, works as a trainer at a leading robotics startup. He is one of hundreds of robot trainers across C...