$modx->setPlaceholders(array(
   'rating_count' => $middle,
   'rating' => $result,
   'ratingCount' => "(".count($all).")"
));

return $middle;

будем благодарны вам за публикацию решения

<?php
$d1 = $id;

&where=`{ "template":9 }`

[[!pdoResources?
    &parents=`319`
    &templates=`9`
    &tpl=`product`
    &includeTVs=`price,image,opisanie`
    &limit=`20`
]]

$modx->getPlaceholder('id')

<div><span class="reviews_param_value stars" data-rating="[[!Test2? &id=`[[+id]]`]][[+rating_count]]" data-num-stars="5"></span></div>
            </div>

<?php
$d1 = $modx->getPlaceholder('id');



$sql = "SELECT C.properties AS prop FROM modx_tickets_comments C LEFT JOIN modx_tickets_threads D
ON C.thread=D.id WHERE D.resource = ".$d1;


$q = $modx->prepare($sql);
$q->execute(array(0));
$arr = $q->fetchAll(PDO::FETCH_ASSOC);
foreach ($arr as $arr_one) {
    $tmp = json_decode($arr_one["prop"], true)["starrating"];
    $all[] = $tmp;
}
$middle = number_format(array_sum($all)/count($all), 1, '.', '' );
if (count($all) == 0) {
   $result = ""; 
} else {
$result = '<span itemprop="review" itemscope itemtype="http://data-vocabulary.org/Review-aggregate"><span class="stars"
 itemprop="rating">'.$middle.'</span>Рейтинг '.$middle.' на основе <span itemprop="count">'.count($arr).'</span> отзывов</span>';


}

$middle = $middle== "nan" ? 0 : $middle;



$modx->setPlaceholders(array(
   'rating_count' => $middle,
   'rating' => $result,
   'ratingCount' => "(".count($all).")"
));

$(document).on('pdopage_load', function(e, data) {
	$('.stars').stars();
});