There seems to be some confusion about who is notified when a note is added to a request or incident ticket in ServiceNow.
To send a message to the user of a ticket (that is, the requester or caller), just add a Public note to the ticket. An email message containing the note will then be sent to the user, and also to anyone who is on the Watch list of the ticket.
If any files need to be sent to the user or there are other intended recipients then an email message should be sent by clicking on the Compose Email button in the top right of the ticket.
Any information relating to the ticket but not appropriate for the user, such as technical details for example, should be added as Work notes. An email message containing the note will be sent to the assignee (unless the note was added by that person). Those on the Work notes list of the ticket will also be sent the note in an email message. Normally though, the user will not be sent the note.
By the way, any verbal conversations with the user about the ticket should be recorded as notes in the ticket, although whether they should be Public notes or Work notes will depend on whether or not the user needs a confirmation of what was said.
In each case, a record of the note or email message, as well as who it has been sent to, is stored in the ticket’s Activity log.
The best practice guide at UoS-iSolutions-IcM004-I Incident Management and Request Fulfilment Best Practice covers this in sections 2.4, 2.8, 3.4.2, 5.2.1 & 5.2.2.