In a small bowl, combine brown sugar, smoked paprika, chili powder, garlic powder, onion powder, salt, black pepper, cumin, and cayenne pepper to create the dry rub.
Pat the pork shoulder dry with paper towels and generously coat all sides with the dry rub, pressing it into the meat.
Place sliced onions in the bottom of your slow cooker, then place the seasoned pork shoulder on top. Pour chicken broth and apple cider vinegar around the pork.
Cover and cook on LOW for 8-10 hours or HIGH for 4-5 hours, until the pork is fork-tender and reaches an internal temperature of 195-205°F (90-96°C).
Remove the pork from the slow cooker and discard the liquid (or reserve for other uses). Use two forks to shred the pork into bite-sized pieces.
Return shredded pork to the slow cooker, add BBQ sauce, and toss to coat evenly. Keep warm on LOW setting until ready to serve.
Serve pulled pork on toasted buns with optional coleslaw and pickles. Enjoy immediately while hot and tender.
