Final answer:
The nurse should report the missing patient assignment notebook to the appropriate authorities and take steps to prevent a similar incident in the future.
Step-by-step explanation:
The nurse should report the missing patient assignment notebook to the appropriate authorities, such as his supervisor or the information desk, as it contains sensitive patient information. Additionally, the nurse can take steps to prevent a similar incident from occurring in the future, such as keeping the notebook secure or using electronic patient record systems.