In a small bowl, combine the smoked paprika, chili powder, garlic powder, onion powder, dry mustard, kosher salt, cumin, and black pepper for the spice rub.
Place the country-style pork ribs into the bottom of your slow cooker in a single layer (as best as possible) and rub with the 2 tablespoons of the spice rub, making sure that the rub covers all the meat. Top with the chopped onions.
In a large bowl, stir to combine the soda/cola, barbecue sauce, and liquid smoke until evenly incorporated. Pour over the pork ribs and chopped onions. Make sure that the sauce completely covers the meat.
Place the lid tightly onto the slow cooker, set the slow cooker to LOW for 8 to 9 hours. Remember not to open the lid during cooking.
Once your ribs have cooked (they should be ‘fall off the bone’ tender), you can remove them to a serving dish.
Pour the cooking liquids into a medium-sized pot and boil for 8 to 10 minutes, stirring frequently, or until the liquids have been reduced by half. This will give you a nice thick sauce to pour over your platter of country-style pork ribs before serving. Alternately, if your slow cooker has a saute setting, you can just leave the liquids in the slow cooker and bring it to a boil right inside the slow cooker.
Pour or brush the sauce over your ribs before serving.