I have a knot on the right side of my nrck. It had been there for awhile. What could this be? It is not painful. I also have kidney cancer

Have it checked! In patients who have a history of cancer, any lump or "knot" should be brought to the attention of their oncologist. Having said that, it is not common to have kidney ca metastasize to the head/neck but it can happen. So definitely, have it checked out!
Biopsy. Are you concern more of the knot or cancer of the kidney. My advice for you is to have the knot in your neck biopsied. You know my recommendation is to have a kidney specialist to assess your kidney cancer and let me know as soon as possible so i can give you a solution or solutions.
Many things. This can be many things. Depending on when you had kidney cancer, the stage and treatment, kidney cancer can lead to subcutaneous (under the skin) nodules. It should be checked out by your oncologist if you have one.