Speck is fat, usually from the rump or hip of a pig. It is cured and often smoked. It is not used for eating, but like lard for frying, and for lardening lean roasts.
Speckschinken is about the same as bacon, meaning a bit meat with a lot of fat from the back or the hip of a pig, often cured and smoked, raw, or cooked.
A Kasseler or Kassler is a smoked, cured pork chop. It's similar to ham steak. Rib meat, neck, shoulder, and belly meat are commonly used. Each variant has a specific name. Kassleler is eaten either like a chop, often with kale, with potatoes, or with sauerkraut, or the meat is cubed and put into stews. Kasseler may be baked, roasted, or boiled. It may be eaten cold. Smoked pork chops (usually fully cooked) are a suitable substitute for Kasseler and can be bought anywhere in the US.