Bring a pot of water to a boil; add pork belly. Cook until pork belly softens, about 5 minutes. Drain and cool pork until easily handled, 5 to 10 minutes. Cut into 2-inch chunks.
Heat vegetable oil in a large pot over medium-low heat. Add cinnamon stick and star anise; fry until fragrant, about 30 seconds. Stir in pork belly, light soy sauce, Shaoxing wine, dark soy sauce, sugar, and garlic. Reduce heat to very low and simmer, stirring occasionally and adding water if sauce reduces too quickly, until pork is tender, about 50 minutes.
Increase heat slightly and continue simmering until sauce reduces to a sticky consistency, about 10 minutes. Remove cinnamon stick and star anise; discard.