Would bone cancer in the chest or back show on a chest xray. severe left upper back/shoulder/chest pain not yet diagnosed. now daily pain unbearable.

Bone cancer: Likely such a cancer would show up on a chest x-ray if not very small. No test is so good that it is 100% sensitive.

See a doctor: Please see a doctor as soon as possible. There are several more common diagnoses (other than bone cancer) that present the way you describe, some of them require rapid treatment for the best possible outcome. To answer your question however, "bone cancer" is sometimes, not alway seen on a chest x-ray. I hope this helps.