Final answer:
The nurse should place the client in the supine position for optimal access and visualization during a bladder scan to assess bladder volume.
Step-by-step explanation:
When assessing bladder volume with a bladder scanner, the recommended position in which a nurse would place a client experiencing urinary frequency is the supine position. This is because, when a person is supine, with the upper limbs, including palms, touching sides and lower limbs touching at sides, this allows for optimal access and visualization of the bladder. It is important for the client to be comfortable and still during the scan to ensure accurate measurements.