Get your self to a doctor (did you have a post-op apt?)
Without actually seeing this can only geuss, two things,
1) this could be dried blood. have you gently cleaned this area since surgery?
2) if this was an entry point for a laproscopic proceedure it could be possible you have developed an infection there which has begun to kill off the skin in , turning it black.
If number two is the case, you will need anti biotics.
things to look out for
Is there anything leaking from this area?
Is the area surrounding it red? or are there any red tracking area radiating from it?
Do you feel feverish or unwell?
either way show your doctor
SEE A DR that could necrosis of the tissue which can spread and turn systemic requiring hospitalization . if it was just bruising thats normal but a foul smell never is . you need antibipotics
sounds like u have an infection u need to see ur doctor