Rinse fresh shiitake mushrooms under running water; Drain them; Trim off the stems; Slice them.
Rinse luffa under running water; Peel it with a Y-shaped peeler; Trim a bit off each base; Cut the remaining into chunks.
Wipe-clean tofu skin with damp kitchen paper; Tear it into few pieces.
Rinse and drain dried goji berries.
Rinse, drain and slice ginger.
Rinse pork shank under running water; Pat-dry it with kitchen paper.
Fill a deep pan with water; Add the ginger; Bring to the boil over a high heat; Scald the pork shank all over in a colander with the boiling ginger water for 3 minutes; Immediately remove it; Rinse it under running water till cool; Drain it.
Fill a stockpot with 2.5L water; Bring to the boil over a high heat; Add all the ingredients; Bring to the boil over a high heat again; Turn to a medium heat; Cover the pot with its lid; Cook over a medium heat for 1 hour; Scoop scum off with a perforated skimmer; Stir seasonings into the soup; Turn off the heat; Arrange the soup into serving bowls; Read to serve.