Place the pork shoulder in the slow cooker. Add the sliced onion, minced garlic, cumin, chili powder, salt, pepper, and chicken broth around the meat.
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. Return the shredded pork to the slow cooker and stir it into the juices.
In a mixing bowl, combine the diced pineapple, finely diced red onion, chopped cilantro, lime juice, and minced jalapeno if using. Stir gently to mix.
Warm the corn tortillas and fill each one with a portion of the pulled pork. Top with a generous spoonful of the pineapple salsa.