Combine pig's feet, cubed pork, and water to cover in a large Dutch oven. Bring to a boil. Reduce heat; cover and simmer 2 hours or until meat is tender. Drain well, reserving 4 cups broth.
Remove meat from pig's feet; discard bones. Combine pig's feet meat and cubed pork; grind together using coarse blade of meat grinder. Set ground pork mixture aside.
Strain reserved broth into top of a double boiler. Place over boiling water; add cornmeal, and cook over boiling water 5 minutes, stirring constantly.
Add ground pork mixture, onion, salt, sage, and pepper; stir well. Cook over boiling water 1 hour, stirring occasionally. Spoon mixture into a lightly greased 8 1/2- x 4 1/2- x 3- inch loaf pan. Cover and refrigerate several hours or until set. Cut into thin slices, and serve cold.
Note: Scrapple may be sliced thin, and pan fried until browned, if desired.