The article states there should be an overflow icon in the article header, but there is not.
Knowledge Management - Service Portal plugin (com.snc.knowledge_serviceportal) is not active.
The documentation referenced is associated with the Knowledge Management Service Portal. Here is a link to the docs on this topic:
Knowledge Management Service Portal
The first step to take will be to active this plugin as it is not activated by default:
Activate the Knowledge Management Service Portal plugin
Once this plugin is enabled, the user action feature will be available within the KM service portal provided by the plugin.
Configure a user action for the Knowledge Management Service Portal article view page