Pat pork shoulder dry and place in a slow cooker. Pour root beer over pork.
Mix together brown sugar, cumin, paprika, salt, pepper, garlic powder, onion powder, and oregano in a small bowl until thoroughly combined. Sprinkle on top of pork and rub lightly until entire surface of pork is coated.
Cook on Low for 5 hours. Switch to High and cook until meat is tender and can easily be pulled apart with a fork, about 3 hours more. Carefully remove pork and shred with 2 forks. Drizzle some liquid from the slow cooker over pork to moisten.