Soak the dried peas for a few hours in a few quarts of water. You can do this overnight if it's easier. Drain and rinse the peas, then put in a stockpot and cover with water (about 2 inches higher than the peas).
Put the ham bone, hock, or salt pork in and bring to a boil. Add the onions, collard greens, and pepper. Reduce heat and cover the pot, leaving the top ajar a bit. Simmer for at least 1.5 hours, until the peas are softened. (Yes, the collard greens get cooked that long too!)
If you used a meaty ham bone, remove that and let it cool so you can take the meat off it, Chop the meat and return to the pot.