In a large bowl, mix together the sugar, onion powder, garlic powder, paprika, cumin, salt, and pepper.
Brush the pork with the liquid smoke and then roll in the bowl with the spices to coat. Set aside.
Place the onion wedges in the Instant Pot, round sides down. Add the soda and lay the pork pieces on top of the onion.
Secure the lid, move the valve to the sealing position, and hit Manual or Pressure Cook on High Pressure for 60 minutes. When done, allow a 10-minute natural release, followed by a quick release.
Transfer the pork and onion to a mixing bowl. Reserve 1/4 cup of the juices from the pot and discard the rest.
Shred the pork and onion with a pair of forks or a hand mixer, and mix in the reserved juices and barbecue sauce before serving with some slaw in rolls or buns.