Final answer:
The nursing assistant should report the blood pressure reading to the patient's nurse.
Step-by-step explanation:
The BEST action the nursing assistant can take when noting a patient's blood pressure of 148/96 is option B: Report the reading to the patient's nurse. Reporting the reading to the nurse ensures that the patient's vital signs are properly documented and that any necessary intervention or further assessment can be initiated by the nurse or other healthcare professionals.