What does a skin cancer lump/bump look like?

See an expert. For skin cancer diagnosis. Just looking at a lesion can let many experienced dermatologists or plastic surgeons make a "probable" diagnosis, but biopsy and microscopic verification is needed to be sure. Not only that, but complete removal is determined by microscopically checking the edges, and then expert reconstruction or skin closure in layers by a plastic surgeon will leave the least scarring.
See below. That is difficult to answer if you are talking about melanoma then you are looking for a raised nodule that is either pigmented or colorless-depigmented. The nodule should be larger than 1.2 cm in dimension. Oter skin cancers are elevated, may be yellow to red and may ulcerate.