Final answer:
The priority nursing action to enhance oxygenation in a patient with unilateral malignant lung disease is to elevate the head of the bed.
Step-by-step explanation:
The priority nursing action to enhance oxygenation in a patient with unilateral malignant lung disease is to elevate the head of the bed. Elevating the head of the bed helps improve lung expansion and reduce the work of breathing, allowing for better oxygenation. It also reduces the risk of aspiration and promotes drainage of secretions.