In a stock pot, simmer the beef shank for at least an hour or until tender.
Remove the scum that rises above the soup. Add more hot water if necessary.
When meat is fork tender, add the onion, salt, whole peppercorn, potatoes and corn. Let stand for 5-8 minutes.
Add the cabbage, chinese cabbage and bokchoy. Season with fish sauce according to taste.
Remove from heat. Serve hot. Enjoy!