Checkout form, how to find out what CODE values ​​are specified in the $arFields array?

Question

1C-Bitrix

I need to know the values ​​of the form fields in the $arFields array, namely the value of the CODE keys. To add fields and register in init.php file.

It is not possible to display the value of the $arFields array, I add the code to the init.php file

$id = intval($_REQUEST["ID"]);
if ( CModule::IncludeModule("iblock") && !empty($id) )
{
    $arSelect = array("ID", "NAME", "PREVIEW_TEXT","CODE");
    $arFilter = array("IBLOCK_ID"=> 25,"SECTION_ID"=>$id);
    $res = CIBlockElement::GetList(Array(), $arFilter, false, false , $arSelect);
    while( $arFields = $res->fetch() )
    {
        echo '<pre>';
        var_dump($arFields);
        echo '</pre>';
    }
}

but I don't see this array output in the checkout page.

Can you please tell me how to find out the values ​​of this array and how to display them on the page? Or in what file could they be assigned CODE values?

Checkout form, how to find out what CODE values ​​are specified in the $arFields array?