Combine water, ham hock, bullion cubes, salt, garlic, and onion in a large pot and bring to a boil.
Carefully add collards allowing them to cook down a minute or two to allow the rest to fit into the pot.
Cover and cook for 1.5 to 2 hours, stirring every now and then, or until the collards are tender. When ready to serve, stir in the vinegar. If you'd like, remove the ham hock and shred the meat. Return the meat to the greens and serve.