Hello! That eye looks very dry and sore to me and whatever is causing this, deserves the attention of a vet. The surface looks to be taccy rather than moist and must be impacting on the dogs' welfare; this is my main take-home message.
As for what the lump could be, it could be the zygomatic salivery gland or a lump to this or other local structure; it could be infection or cancer from any of the surrounding tissues. It could be infection associated with a underlying tooth root. It could be a lymph node eg in infection or lumphoma. It could be a bony lump. Your vet will be able to examine the lesion more closely than I can and examine it within the context of the whole patient. They will then know more than I can glean from herr and be able to offer advise regarding the best way forewsrd. I feel that given how dry the eye looks, this conversation should take place sooner rather than later; can you get in later today?