Get data posted from Ninja Popup using hook and use data captured for other purpose.

learnwithbisht-get-ninja-popup-data.php

/**
* Code to get data posted from ninja popup.
*/
add_action( 'ninja_popups_send_form', 'learnwithbisht_ninja_popups_send_form', 10, 1 );
function learnwithbisht_ninja_popups_send_form( $filterAndActionData ) {
	$post_data = $filterAndActionData['data']['post'];
	$popup_ID = $post_data['popup_ID'];
	$email = $post_data['email'];
	/** write code here to use data as per requirement **/
}