Final answer:
To gather more data about a pulsating mass in a client's periumbilical area, the nurse should auscultate the area.
Step-by-step explanation:
When a nurse notes a pulsating mass in a client's periumbilical area, the appropriate action to gather more data about the mass would be to auscultate the area. Auscultation involves using a stethoscope to listen to internal sounds of the body. This can help the nurse identify any abnormal sounds associated with the pulsating mass, which can aid in making a diagnosis.