Sprinkle 3/4 of the onion and garlic into the bottom of a roasting pan; pour in the vinegar and water. Season the neck bones with salt and pepper and place into the roasting pan. Sprinkle the remaining onion and garlic over the neck bones; cover the roasting pan tightly with aluminum foil.
Bake in the preheated oven for 2 hours, basting every 30 minutes. Be sure to recover the foil every time you baste. After 2 hours, remove the foil and continue baking until the neck bones are golden brown, about 45 minutes.