Final answer:
The nurse should instruct the client to push the button themselves or ask a family member to push it when experiencing severe pain.
Step-by-step explanation:
The nurse should provide the teaching point D to the client: "If you feel severe pain, either push the button yourself or ask one of your family members to push the button." With patient-controlled analgesia (PCA), the client has control over administering their pain medication, ensuring that they receive relief when needed. By pushing the button when experiencing severe pain, the client can effectively manage their pain without risking an overdose or addiction.