If a CNA finds that a diabetic patient _________, he or she must inform the nurse as soon as possible.

When a diabetic patient fails to eat anything at lunchtime, this can significantly impact their blood sugar levels, potentially leading to a dangerous condition like hypoglycemia. Managing nutrition and meal timing is crucial for diabetics, as inconsistent eating patterns can result in fluctuations in glucose levels that may require immediate attention. By informing the nurse promptly, the CNA ensures that the patient's health is closely monitored, and appropriate interventions can be initiated to prevent complications.

In the context of the other options, while each situation may require attention, they do not pose the same immediate risk to the patient's health related to diabetes management. Combing hair at odd times, reporting numbness in the feet, or refusing to finish writing a will may indicate other concerns, but they do not directly affect the critical management of a diabetic patient's dietary needs and blood sugar stability.