Final answer:
The nurse should instruct the client taking enalapril 20 mg PO daily to monitor for orthostatic hypotension.
Step-by-step explanation:
The nurse should instruct the client taking enalapril 20 mg PO daily to monitor for orthostatic hypotension. Enalapril is an angiotensin-converting enzyme (ACE) inhibitor that can cause a decrease in blood pressure when changing positions, leading to orthostatic hypotension. This can result in symptoms such as dizziness, lightheadedness, or even fainting.