In the TalkJS Dashboard you have the ability to allow or forbid your users from mentioning other users. The ability to use mentions is tied to to user Roles, meaning you can allow certain groups of users to mention other users, while forbidding others. See here:
Once the mentions are enabled, you can use them by entering an
@ sign into the Message field.
Give them a try, by typing
@ into the chat:
When mentions are used, you can set it up, so that users will only receive a notification once they are mentioned. Changing the notification settings is described in more detail on the page about Participants.