Final answer:
The nursing diagnosis to prioritize for a client prescribed cyclobenzaprine is 'risk for injury related to CNS depression' due to potential side effects like drowsiness and impaired motor functions that increase the risk of falls or injuries.
Step-by-step explanation:
Given that the 29-year-old client has been prescribed cyclobenzaprine, a muscle relaxant that can cause central nervous system (CNS) depression, the nursing diagnosis that should be prioritized is a risk for injury related to CNS depression. Cyclobenzaprine may cause drowsiness, dizziness, and impair cognitive and motor functions, increasing the risk of falls or other injuries. For this reason, the nurse needs to monitor the client's response to the medication and take preventive measures, such as assisting with ambulation and advising the patient to avoid activities that require mental alertness or coordination until they know how the medication affects them.