Hello Lenykeksik.
Thanks for your feedback.
All data is stored in the database of your WordPress instance as a meta value associated with the post of type shop_order.
This means you can use the wordpress function get_post_meta to retrieve the data of all fields configured for your checkout forms, internal and custom fields if you don’t have a valid WC_ORDER object available. In this case you will need the Order ID and you could retrieve the values stored with
$email = get_post_meta([order_id], '_billing_email', true);
If you have access to a valid Order object constructed by the class WC_ORDER you can use the field name of a default WooCommerce field like _billing_email to retrieve the value.
$value = $order->billing_email;
For custom fields you can use the field name as indicated in the settings of WooCommerce Poor Guys Swiss Knife in the Billing or Shipping Section
$value = $order->billing_your_sanitized_custom_field_name;
or
$value = $order->shipping_your_sanitized_custom_field_name;
Don’t forget to assure yourself that you have constructed the $order object with an order id otherwise you have to assure to load a valid order first.
Hope this answer helps you with your code.
Regards.
uh