Dr ordered a nerve conduction study of my leg. would it show that i have a herniated disk? have pain / numbness in both calves / bottom of feet.

Nerve damage : The NCS, especially if accompanied by EMG will determine if there is any nerve abnormalities and (EMG) muscle abnormalities. Peripheral or compression neuropathies will suggest pathology, but CT or MRI would definitively reveal a herniated disc, spinal compression (stenosis) or other pathology. This combination is ideal to determine the answer to your questions