Place the sliced onion in an even layer at the bottom of the slow cooker.
Set the pork shoulder on top of the onions.
In a small bowl, stir together the barbecue sauce, apple cider vinegar, minced garlic, paprika, salt, and black pepper.
Pour the sauce mixture over the pork, making sure it coats the meat evenly.
Cover and cook on low for 8 hours until the pork shreds easily with a fork.
Remove the pork from the slow cooker and shred it with two forks, then return it to the cooker and stir it into the sauce.
Spoon the pulled pork onto the slider buns and serve.