How to inspect/access config values specified in config/email.php?

The docs you linked to say that if you name the config file /config/email.php, that it will use it automatically.

If you prefer not to set preferences using the above method, you can instead put them into a config file. Simply create a new file called the email.php, add the $config array in that file. Then save the file at config/email.php and it will be used automatically. You will NOT need to use the $this->email->initialize() method if you save your preferences in a config file.