Final answer:
The nurse should identify option A, 'I will wash the ink markings off the radiation area after each treatment,' as an indication that the client understands the teaching about radiation therapy for esophageal cancer.
Step-by-step explanation:
In order to determine if a client understands the teaching about undergoing radiation therapy for esophageal cancer, the nurse should identify the statement that accurately reflects the client's understanding. Out of the given options, the nurse should identify option A, which states, 'I will wash the ink markings off the radiation area after each treatment,' as an indication that the client understands the teaching. This response shows awareness of the importance of washing off the markings that indicate the radiation area, which is necessary for accurate treatment delivery.