To display a Read More button on a page, you'll need to make sure the long description of the event content is enabled and has information in it.
To confirm an event category has long description enabled:
Go to onMessage > Content > Events.
Click on the appropriate event category.
Select "Show Long Description".
Click Save & Close.
This will display any content that has been added to the Description box of the specific event.
Note: This will need to be done in the *primary* category that the event is published to. Enabling 'Long Description' in a category that the event is shared/published to -but is not the primary- will not provide you with the needed 'description' field in the event's settings.