Place the sliced onion in a slow cooker. Set the pork on top and season with smoked paprika, garlic powder, salt, and pepper.
Whisk broth, barbecue sauce, vinegar, and brown sugar; pour around the pork. Cover and cook on LOW for 8 hours, until fork-tender.
Transfer pork to a board and shred with two forks, discarding excess fat. Skim excess fat from the cooking liquid, then stir in enough liquid to keep the pork moist.
Pile pulled pork onto buns, add extra barbecue sauce and coleslaw, and serve warm.