From Aspen Documentation
Determines the parent of the current module, mainly for navigation purposes.
Since 1.0
Arguments
string getParentModule ()
Returns
Returns a string.
Examples
First, you need to set a function within your module class that reports it's parent module. This function must be called "whosYourDaddy".
public function whosYourDaddy(){ return 'Blog_Admin'; }
Then calling this function will return the parent:
$this->APP->router->getParentModule();