In a large pot over medium heat, bring enough water to cover meat into a boil. Add beef shanks and continue to boil for about 10 minutes, skimming scum that accumulates on top. Remove meat from water and wash under cold water to remove impurities. Discard liquid and rinse pot.
In the pot over medium heat, return meat and enough water to cover. Bring to a boil, skimming scum that accumulates on top. When the broth has cleared, add onions, garlic, peppercorns and fish sauce.
Lower heat to low, cover and cook at a bare simmer for about 3 hours or until meat is fork-tender. Season with salt to taste.
In a medium pot over medium heat, bring about 4 cups water to a boil. Add cabbage and cook for about 1 to 2 minutes or until tender yet crisp. With a slotted spoon, remove from water and set aside.
In another pot over medium heat, bring about 4 quarts water to a boil. Add egg noodles and cook for about 10 to 15 seconds. Remove from water and rinse with cold water. Drain well.
Divide egg noodles into serving bowls. Add beef shanks and cabbage. Pour hot broth. Garnish with fried garlic bits and chopped onions. Serve hot.