My cat ran away yesterday afternoon; I got it back but found a red dot on its body

From the photo, if the red dot is on the abdomen it may be a nipple, a normal structure usually placed symmetrically along the middle of the belly. Carefully check whether there are scales, scabs, abnormal patches, hair loss, or itch around it.

If it is not a nipple and you see those abnormal signs, it is likely a skin infection; take the cat to a vet for a skin scraping and Wood’s lamp exam to diagnose and treat.