Final answer:
The nurse should first remind the student that strength testing should be performed on both sides of the body to ensure a comprehensive assessment when evaluating a stroke patient.
Step-by-step explanation:
In the scenario where a nursing student is performing a neurologic assessment on a patient who sustained a stroke, the nurse observes the student evaluating grip and hand strength only on the affected side. The correct first action for the nurse would be to remind the student that strength testing needs to be done bilaterally. This ensures a comprehensive assessment, as muscular strength should be compared between both sides to detect any lateral differences in strength, which could indicate a deficit in one corticospinal tract versus the other.