From above it looks like some kind of growth or tumor but from the side it looks like an injury were the scales have been torn off.
One of my small Koi got attacked by a Dragonfly larve which managed to pull of a few scales and injure the koi, this may be the case? Or it could be a number of other things, if the water is fine I would leave it for a few days and watch the fish carefully, there is no need to stress it out by trying to catch it or medicate unless you are sure of what you are treating. Can you get some more side on and birds eye view pictures of it in the pond? How is it acting in general?