Mix all the rub ingredients in a small bowl.
Pat the pork dry and press the rub all over the surface.
Optional: sear the pork on all sides in a hot oiled skillet, 2 to 3 minutes per side.
Scatter the onion in the slow cooker and set the pork on top.
Whisk the broth, vinegar, Worcestershire, and liquid smoke. Pour around the sides of the pork.
Cover and cook on LOW 8 to 10 hours or HIGH 5 to 6 hours, until the pork shreds easily (200 to 205°F).
Shred with two forks and discard large pieces of fat.
Skim the fat from the juices and toss about ½ cup of juices with the pork.
Serve on toasted buns with sauces on the side, coleslaw, and pickles.