Place pork and chicken bones in a large stockpot and cover with cold water. Place on a burner over high heat and bring to a boil. Remove from heat as soon as boil is reached. While pot is heating, heat vegetable oil in a medium cast iron or non-stick skillet over high heat until lightly smoking. Add onions, garlic, and ginger. Cook, tossing occasionally until deeply charred on most sides, about 15 minutes total. Set aside.