Yes, cats do have belly button which looks like a tiny scar.
It is generally difficult to find, located about midway down the abdomen, just below the ribs.
Similar to humans, a kitten is also attached to her mother through the umbilical cord for the transport of oxygen and nutrients.
Once the kitten is able to breathe air, the mother will lick or bite the cord to detach. This cord dries up and falls off to leave a tiny scar.
Due to the small scar size (5mm) and also covered with fur, it is difficult to see.