Rub chicken feet with salt, rinse, and drain well. Using a knife or kitchen shears, cut ends to remove nails.
In a pot over medium heat, bring about 6 cups of water to a boil. Add chicken feet and pounded ginger. Cook, skimming any scum that floats on top. for about 20 to 25 minutes or until chicken feet are tender.
Drain and rinse chicken feet with cold water. Discard liquid.
In a pot over medium heat, heat oil. Add onions, garlic, and ginger and cook until softened.
Add chicken feet and cook, occasionally stirring, for about 2 to 3 minutes. Add fish sauce and cook for 1 to 2 minutes.
Add rice and cook, stirring regularly, for about 1 to 2 minutes.
Add about 10 cups of water and bring to a boil, removing scum that may float on the top.
Add bouillon cubes and stir until dissolved.
Lower heat, cover, and simmer, stirring occasionally and adding additional water in 1/2 cup increments if needed, for about 30 to 40 minutes or until rice is softened, congee has thickened to desired consistency, and chicken feet are tender.
Season with salt and pepper to taste.
Ladle into serving bowls and top with green onions, fried garlic bits, and drizzle with calamansi juice as desired. Serve hot.