Jackeline, I wonder why you ask if this is a trick question. Of course it is not a trick question. To say that dogs do not have belly buttons (an umbilicus) is totally wrong. . How do you think they receive their nutrients in the womb. In the same way as we do of course.
Is this a trick question ? Dogs do not have belly buttons . If you are referring to a nipple or aureole it could be an infection , so best have your puppy seen by a vet .