I have a small red bump on my left leg, above my knee. it's become shiny and dry. it's been there for over a month. it doesn't hurt but feels tender.

Unfortunately it is: impossible to diagnose lumps, bumps and rashes over the internet since we can't see or examine the area in question. It could be an infection, cancer or any of a number of things. You need to make an appointment with a health care provider to examine and evaluate you. Make an appointment today.

See dermatologist: should be examined by dermatologist to make certain that it is nothing serious. From what you stated, it seems to be a benign entity like a wart, but you need to make sure.