Final answer:
When assessing a patient complaining of diplopia, it is most pertinent to ask about his medical history related to the condition, such as a history of conditions that may cause diplopia and any recent changes in medications or eye-related symptoms.
Step-by-step explanation:
When assessing a 59-year-old male who complains of diplopia, it is most pertinent to ask about his medical history related to the condition. Specifically, it would be important to ask if he has a history of conditions that may cause diplopia, such as diabetes, high blood pressure, stroke, or head injury. Additionally, asking about any recent changes in medications or eye-related symptoms, such as eye pain or redness, would also be relevant.