Lump above collar bone is this cancer? xray clear. no other symptom?

That will be the main concern and the first entity to be ruled out with many other benign causes more likely and commonly seen. Seeing your doc and adopting a strategy, either watchful waiting, possible treatment if an immediate source is found, such as a local infection or inflammation or proceeding with further tests and possible excision/ biopsy would be best at this point.

Strongly recommend a complete evaluation by your internist (NOT a GP), along with whatever testing is indicated by the evaluation. Further testing may be indicated or a biopsy may be necessary. If you are a smoker, you should make your appointment today and not wait.