Final answer:
The latest step in a wet hair service is examining the client's hair and scalp, which is done after draping and before shampooing and conditioning to assess the client's specific hair needs.
Step-by-step explanation:
The step that would occur the latest when performing a wet hair service inclusive of draping, shampooing and conditioning is c) examining the client's hair and scalp. This step typically takes place after the client has been draped and before the actual washing process begins. Draping is one of the initial steps to protect the client's clothing, which includes turning the client's collar inward. Testing water temperature and pressure would be done just before applying shampoo to ensure comfort and safety. Therefore, the examination of the hair and scalp is done prior to these steps to assess the client's needs and any specific conditions that might affect the choice of shampoo or conditioning treatment.