In a large pot or Dutch oven, combine the ham hock, chicken broth and diced onion. Bring to a gentle boil, then reduce to a simmer. Let it cook for about 20-30 minutes to start pulling out that smoky flavor.
Pile in the collard greens. It will look like too much at first, but they’ll cook down quickly. Stir to coat them in the broth.
Add garlic, vinegar, sugar and red pepper flakes. Partially cover and simmer on low heat for 1.5 to 2 hours, stirring occasionally. The greens should be soft, silky and deeply infused with flavor.
Remove the ham hock, shred the meat, and return it to the pot, discarding the bone and excess fat. Taste and season with salt and black pepper as needed.
Spoon into a bowl with plenty of the potlikker. Serve hot as a side or alongside cornbread to soak up every drop.