Will non contrast ct brain scan show osteoma or meningioma in skull vault right occipital or will contrast ct be required?

Comes down to resolution. If lesion is large enough, should readily be imaged, and contrast could be employed to be certain if ambiguities are present. You could certainly discuss this with the radiologist at time of the procedure.

You should have CT with contrast if there is no absolute contraindication with IV contrast because of these facts: The nonenhanced CT examination detects 85% and contrast-enhanced CT detects 95% of all intracranial meningiomas. The IV contrast also helps to differentiate the meningioma from the osteoma of the inner table of the skull.