Final answer:
The nurse should document the findings on the admission sheet.
Step-by-step explanation:
The best action for the nurse to take is to document the findings on the admission sheet.
The nurse should document the presence of small, circular, ecchymotic areas on the client's knees as part of the initial physical assessment. This is important for maintaining accurate and complete medical records.
By documenting the findings, the nurse ensures that the information is recorded and can be used for future reference and continuity of care.