1For the stock: Place bones, onions, garlic, ginger, fish sauce, and turnip in a large pot. Add 5 quarts water and slowly bring to a boil over medium heat, skimming any foam. Lower heat; simmer for 2½ hours.
2For the soup: Place cloud-ear fungi in a medium bowl and add boiling water to cover, and soak until softened, about 10 minutes. Drain, wash, and roughly chop.
3Strain stock, and skim any fat from top.
4Heat eight cups of stock in large saucepan over medium heat.
5Add cloud-ear fungi and simmer for 3 minutes.
6Add pork, fish balls (if using), and greens, keeping stock at a low simmer for 5 minutes. Bring a medium pot of water to a boil and cook noodles for 3 mins, gently separate with a fork.
7Drain and add to soup.
8Serve in individual bowls, garnished with scallions and cilantro. Serve with Chile Fish Sauce on the side, to be added to taste at the table.