Can you see a bone tumor on an xray?

Sometimes: I assume you are referring to a primary tumor of the bone rather than a tumor that has spread to the bone from another site. It depends on they specific type of bone tumor, the involved bone and the size of the tumor. Sometimes special scans such as a ct or MRI scan are needed to detect a bone tumor.

Usually yes: Most bone tumors, primary and metastatic are visible on x-ray, unless too small or too early.