Heat vegetable oil (1 tablespoon) in a pressure cooker over medium-high heat until shimmering. Add smoked sausage (8 ounces) and cook until starting to crisp around edges, about 2 minutes. Add onions (1 medium) and cook, stirring, until softened, about 3 minutes longer. Add ground cumin (2 teaspoons) and cook until fragrant, about 30 seconds. Add diced green chilies, dried black beans (8 ounces), cilantro (12 stems), chicken legs, and low-sodium chicken stock (1 quart). Season gently with kosher salt and black pepper and stir to combine.
Seal pressure cooker and bring to high pressure. Cook for 40 minutes. Cool pressure cooker under a cold running tap (if using an electric cooker, use the quick release valve), and open. Using tongs, transfer chicken pieces to a bowl. Discard cilantro stems. Return beans to high heat and continue cooking, stirring, until reduced to a thick, stew-like consistency, about 5 minutes. Meanwhile, shred chicken from bones and discard skin.
Stir chicken into beans, season to taste with salt and pepper, stir in half of chopped cilantro, and serve, passing sour cream, lime wedges, and remaining cilantro at the table.