You likely won't be able to test that on our demo site as we block access to query and code actions for security purposes so you won't be able to execute the database queries you'd need to track read status in a custom database table.
You can probably do something simple like increment a field or change a text fields value using a field action to test the trigger behavior as you'd need to act on a Joomla event in the auto action, which is done by prefixing the trigger in CB Auto Actions with "joomla_". See the below Joomla documentation for content events.
docs.joomla.org/Plugin/Events/Content
onContentAfterDisplay would likely be the best place to check this. Then in the auto action condition against [var1] (this is the context variable of that trigger) to make sure it's com_content.article, which is the context of directly viewing an article. This should be without a doubt doable though.