In large bowl, stir together Naranja Agria,oregano, pepper, 3 tsp. Adobo, 2 tsp. cumin and 2 tbsp. garlic; set aside.
Using sharp paring knife, make deep narrow slits all over pork. Transfer pork to large, plastic zip-top bag; scatter onions on top. Pour in reserved Naranja Agria mixture. Push air out of bag and seal; transfer to refrigerator. Marinate at least 8 and up to 24 hours.
Meanwhile, in small bowl, stir together capers, remaining 1 tsp. Adobo, remaining 1 tsp. cumin and remaining 1 tbsp. garlic; set aside.
Heat oven to 400°F. Remove pork and onions from marinade, discarding marinade. Transfer pork and onions to roasting pan just large enough to hold pork. Using fingers or small spoon, open slits in pork and stuff with reserved caper mixture. Pour 1½ cups water into bottom of pan. Roast pork, uncovered, for about 30 minutes. Reduce heat to 325°F; roast until pork is tender when pierced with thin blade of knife, is cooked through (quick-read thermometer will register 180°F when inserted into thickest part of pork without touching bone), and skin is golden brown and crisp, adding water in ½-cup measures if pan becomes dry, about 6 hours.
Transfer pork to cutting board; let stand about 10 minutes. Remove crisped pork skin and coarsely chop. Slice or pull pork into large pieces. Transfer pork to serving platter; top with skimmed pan juices and scatter with crispy chopped skin.