Start by cutting your pork shoulder into 4 pieces.
In a large bowl add the meat and pour the liquid smoke over the pork
Coat all sides with the smoke and do the same with the bbq rub making sure to coat all pieces with the liquid smoke and bbq rub.
Cover and refrigerate for 3-4 hours
Put the meat in the Instant Pot along with the cola and pressure cook for 45 minutes. Let the Instant Pot naturally release for 15-20 minutes.
Remove the meat from the pressure cooker and let it cool. After it's cooled a bit shred with a fork. Reserve some of the liquid to pour over the pulled pork.
Notes
You don't have to shred it all. Not shredding or pulling the pork until ready to use will keep it moist. Either way, keep some of the liquid to mix into the pulled pork.