Final answer:
The nurse should assess the indention and ask the client about its origin while considering the client's cultural background without making assumptions.
Step-by-step explanation:
When a nurse in a clinic observes a circular, dark-pink indention on a client's abdomen, especially with the understanding that the client is not from the United States, the nurse's next best action would be to assess the indention and ask the client about the origin of the circular mark on the abdomen (Option A). This approach allows for the collection of important health history in a respectful and nonjudgmental manner, considering the possibility of cultural practices like cupping but not assuming it outright. By engaging the client with open-ended questions, the nurse can better understand the client's health beliefs and practices, which is crucial when providing culturally competent care.