Hard to see in the pic possibly a bacterial infection. The water is very cloudy signs of something is wrong with the aquarium water. Please ask friend how often do he/she perform water changes and filter maintenance.
Agree with kno4te, looks like a granuloma or tumor. Just as in humans, could be benign, maybe not.
A vet experienced in fish surgery could cut it off.
I edited your photo to help put it in view.
Below are a couple shots of a before, and after similar surgery, from one of my veterinary text books.
Once removed, it can come back, just like cysts on humans.
Guess it comes down to how deep are the pockets($$$).
Tell your friend to up the filtration, lighten the stocking, and do some water changes. That black moor also seems to have popeye and is making its eyes bulge more than normal