Place the pork into a slow cooker. Add sliced onions, and add root beer until the meat is just covered. Cover and cook on Low 7-8 hours - or High 5-6 hours. Checking occasionally.(Times may vary depending on individual slow cooker)
Meat is done when it easily pulls apart and off the bone. Drain root beer, shred pork, and finish with your favorite BBQ sauce. Serve over hamburger buns and enjoy!