Would a tumor caused from lymphoma, e.g. node, etc, show up on plain xray and ct?low back pn, clear l spine xray and ct to look for kidney stones, etc.

Not XR: A x-ray would not be particularly helpful, unless it's a large tumor. Ct would be much better, and should be able to pick up enlarged lymph nodes. Watch out for contrast though. Kidney stone cts are done without IV contrast, but you will need contrast to look for tumor (at least much better at it). Talk to your doctor to make sure whether you are doing it with or without contrast.