Boss Pro: Before Blog Widget
The Boss Pro theme displays a Genesis eNews Extended in the Before Blog widget location. This widget will display at the top of each single post.
You will need to install and activate the Genesis eNews Extended plugin first.
Once you have activated the plugin, go to Dashboard > Appearance > Widgets > drag a Genesis eNews Extended widget to the Before Blog widget location.
The setup of the widget will depend on the third party subscription service you are using. This guide by the creator of the plugin will assist.