A notebook entry can be deleted as follows:
Open the record associated with the notebook, e.g., the applicant or contact or client.
Click View and then click Notebook.
Find and highlight the notebook entry to be deleted.
Hover on the entry for the Client.
Click the "X" to delete it.
Click Yes to confirm the deletion.
Alternatively, from the list: Open the record associated with the notebook, e.g., the applicant or contact or client:
Click Notebook.
Find and highlight the entry to be deleted.
Click More and then click Delete.
If a message appears to tell you that you can't delete it because it is protected, the Protected flag will need to be cleared by the person who created it, which they can do as follows (or a user - most likely a system Admin - with the Permission to unprotect & delete other user's Notebook Items, can delete and unprotect on behalf of any user):
Open the record associated with the notebook, e.g., the applicant or contact.
Click View and then click Notebook.
Find and highlight the notebook entry to be deleted.
Click on the Additional Info tab.
Remove the tick from the Protected box.
This notebook entry can now be deleted as per the original steps above.