Final answer:
The trigeminal nerve (cranial nerve V) is assessed by touching a cotton wisp to the patient's forehead, cheeks, and chin to test the sensory function of its three branches.
Step-by-step explanation:
The cranial nerve that a nurse would assess by touching a cotton wisp to a patient's forehead, cheeks, and chin is the trigeminal nerve (cranial nerve V). This nerve carries the general somatic senses from the head, like touch sensation, as well as controlling the muscles of chewing. Assessing the congenital sensations in the forehead, cheeks, and chin allows for testing the different branches of the trigeminal nerve, which are the ophthalmic, maxillary, and mandibular branches, respectively.