Q: What did the Dalmatian say after eating lunch?
A: Wow, that really hit the spot!
That hit the spot is an idiom meaning something that was needed. In this joke the speaker, the Dalmatian, was hungry and lunch hit the spot: lunch is exactly what was needed.
This joke is funny because it plays with the idea of hitting the spot (the markings on a Dalmatian) and hitting the spot (being exactly what was needed).
If you want to learn more about Dalmatians, this will hit the spot: