Scratch on nose scab hasn't healed in 2 years?

Skin cancer! Until proven otherwise any wound which won't heal within a week or two is very suspicious for a skin cancer. Especially if it is enlarging with time, get it checked out asap.
Could be serious. Wounds that don't heal for a long period need to be checked. You should see your primary care doctor or dermatologist soon. This frequently turns out to be a skin cancer which is very curable.
See your doctor. Skin lesions that don't heal are always a concern for a form of skin cancer (basal cell or squamous cell carcinoma). See your family doctor or dermatologist as soon as possible to confirm a diagnosis.