Place the sliced onion and minced garlic in the bottom of the slow cooker to create a base layer.
Add the pork shoulder on top of the onions and garlic.
In a bowl, stir together the apple cider, brown sugar, cinnamon, nutmeg, cloves, salt, and black pepper until the sugar dissolves.
Pour the cider mixture over the pork, making sure it covers the meat evenly.
Cover and cook on low for 8 hours until the pork is very tender and pulls apart easily with a fork.
Remove the pork from the slow cooker and shred it using two forks, discarding any large pieces of fat.
Return the shredded pork to the slow cooker and stir it into the remaining juices to soak up the flavors.
Serve the pulled pork on the sandwich buns.