@gergana – The line Display TEC ticket meta field value on the order admin page, is just a comment describing the action for the code snippet. You can use the same code snippet to have the attendee ticket info displayed in other areas, by calling the function with a different hook or filter. Examples:
To display on the Woocommerce Admin order screen
add_action( 'woocommerce_admin_order_data_after_shipping_address', 'replace_with_your_function_name', 10, 1 );
To display in order email notifications
add_action( 'woocommerce_email_customer_details', 'replace_with_your_function_name' );