Does a kangaroo have a belly button?

No, kangaroos are not placental mammals, and the belly button is a vestage of where the mother's placenta connects to the fetus.
No, kangaroos are not placental mammals, meaning that they are not connected via an umbilical cord when they are developing in their mother's womb. The bellybutton is merely a scar left from the where the umbilical cord was at. All placental mammals like humans, dogs, cats, etc. have bellybuttons, while marsupials and monotremes, (egg laying mammals, which consists of only 2 species, the platypus and echidna) have no bellybuttons because they are not connected to their mother by an umbilical cord.