In order to mention users on Wiki pages, it is important to make changes in the settings:
Step 1: Activate the preference "Tagging users"
To start activate "Tagging users" by going to Settings > Control Panel then search for "Tagging users" in the search bar, activate this preference and apply the changes.
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Step 2: Activate the preference "User mention notifications"
Activate "User mention notifications" by going to Settings > Control Panel then search for "User mention notifications" in the search bar, activate this preference and apply the changes.
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This will allow users to be notified when they are mentioned on a wiki page.
Conclusion
Once this is done, when a user is mentioned on a wiki page in the format "@username" he will be notified and his information will appear when his name is over the page.