Clean the ox knee bones thoroughly and soak in water to remove blood.
Put the ox knee bones in a pot with water, green onion, garlic, and ginger, then bring to a boil.
Simmer over medium heat for 2 to 3 hours until the bones become tender, then take out the meat.
Cut the ox knee meat into bite-sized pieces.
Strain the soup stock through a cheesecloth to make it clear.
Add the meat and broth to a pot, season with perilla seed powder, soup soy sauce, salt, and pepper.
Boil again until the perilla seed powder is well dissolved.
Serve in a bowl and garnish with chopped green onions.