1. Prepare the cilantro roots by soaking them in water, scraping the skin off, and finely mincing them. Peel the garlic cloves. Combine the prepared garlic, cilantro roots, and whole white peppercorns in a mortar and pestle and pound until a paste is formed.
2. Add the fish sauce, oyster sauce, and dark soy sauce, and palm sugar to the cilantro-garlic-peppercorn paste and mix until all ingredients are combined.
3. Cut the pork shoulder or loin into small, approximately 1/2 inch pieces. Place the pork into a container and rub the marinade paste into it. Cover, refrigerate, and allow it to marinate for at least 2 hours.
4. While the pork marinates, soak the bamboo skewers in water. They should soak for at least 30 minutes before grilling. When the pork has marinated, thread the pork pieces tightly onto the skewers, approximately four to six pieces per skewer. Coat the skewers with any remaining marinade paste.
5. Heat the grill to low or medium low heat. Place the skewers on the grill and allow them to cook slowly until cooked through, turning and basting them periodically with coconut milk. If grilling pork shoulder, this may take 15-20 minutes. For pork loin, it will take slightly less time.