Sternocleidomastoid muscle is supplied by:
The spinal accessory nerve provides the motor supply. It passes through the muscle.
The spinal accessory nerve supplies:

The sternocleidomastoid, the chin turning
The trapezius, the shrugging muscle.

Cervical nerves provide a proprioceptive sensations to these muscles.
Reference: B D Chaurasia’s Head and Neck anatomy, 6th ed page no 384
Vagus nerve
Spinal accessory nerve
Marginal mandibular branch of facial nerve
None of the above