AJAX – Returning Two JSON Objects with One PHP Function

If I get it correctly, You need to wrap them in an array and pass to Javascript.

function get_ldap_attr() {
    header("Content-type: application/json");
    ...

    // suppose you want to return $second_var
    echo json_encode(array($sup,$second_var));
    die();  
}

Success function of JSON request will receive them as array. You can access them with integer index.

jQuery(function() {
    jQuery('#empLanId').on('blur', function() {
        var lan = jQuery('#empLanId').val();
        var ajaxurl="<?php echo admin_url("admin-ajax.php", null); ?>";
        var data = { action: "get_ldap", lan: lan};
        jQuery.ajax({
            type: 'POST',
            url: ajaxurl,
            data: data,
            dataType: 'json',
            success: function(response) {
                response[0] // first $sup variable
                response[1] // second $second_var variable
                //jQuery('#empSupLanId').val(response.lanid);
                //jQuery('#empSupName').val(response.fullname);
                //jQuery('#empSupNumber').val(response.phone);
            }
        });
    });
});