The picture is not close up enough and not clear enough. Having said that, I don't think the word "sore" is the correct word to describe what I do see. Wound/lesion is more accurate.
Diagnoses are time consuming. I just spent about 20 minutes trying to find terms for the anatomy of a cat's face. All I could come up with was that the area the lesion is on is called "anteromedial cheek area" in humans. Maybe that translates to felines, maybe not. I don't know.
I suppose we could say:
Your cat has a lesion on the anteromedial cheek area - but again, the picture isn't close-up enough or clear enough.
Even if you could take a better close up pic - it would still be much better if the area around the lesion was shaved as it looks like the the borders of the lesion are under the hair. I've never tried and I'm pretty sure it's impossible to shave that part of your cat's body without the cat turning into Freddy Krueger or in the attempt harming the cat. Front face is usually a no-no for shaving unless animal is under anesthesia. I've shaved under neck but never front of face.
If you haven't taken your cat to the vet yet - is the lesion showing signs of healing? After a few days and most certainly a week you should see some healing. If it's not getting better, getting worst, or showing signs of infection - a vet visit is the best thing to do.
Note: one of the best ways to keep track of if a wound/lesion is healing is to take daily close-up pictures.