if($_REQUEST['tutid'] && $_REQUEST['cid']){
    //make array to cid to get id
    foreach($_REQUEST['cid'] as $key => $value){

    $res = mysqli_query($dbh,"SELECT * FROM test WHERE id =".$value." AND page_id=".$_REQUEST['tutid']." ORDER BY id DESC LIMIT 1") or die(mysqli_error($dbh));

       $rows =  mysqli_fetch_assoc($res);

       $row[] = array_map('utf8_encode', $rows); //line 80
       $data = array();

       $data['id'] = $rows['id'];
       $data['username'] = $rows['username'];
       $data['description'] = $rows['description'];
       //etc all

           //do something

             if (!empty($data)) {
             echo json_encode($data);
             flush();
             exit(0);
             }
    }
}

if (!empty($rows)) {
    $row[] = array_map('utf8_encode', $rows);
}

<div class="case" data-post-id=".$id."></div>
<div class="case" data-post-id=".$id."></div>
// etc more

<script type="text/javascript" charset="utf-8">

var CID = [];
$('div[data-post-id]').each(function(i){
    CID[i] = $(this).data('post-id');
});

function addrep(type, msg){
CID.forEach(function(id){
    $("#newreply"+id).append("<div class='"+ type +""+ msg.id +"'><ul>"+ msg.description +"</ul></div>");
});
}
var tutid = '<?php echo $tutid; ?>';
function waitForRep(){
    $.ajax({
        type: "GET",
        url: "/server.php",
        cache: false,
        data: {
        tutid : tutid,
        // this way array containing all ID's can be sent:
        cid : CID
    },
        timeout:15000,
        success: function(data){
            addrep("postreply", data);
            setTimeout(
                waitForRep,
                15000
            );
        },
        error: function(XMLHttpRequest, textStatus, errorThrown){
            setTimeout(
                waitForRep,
                15000);
        }
    });
}


$(document).ready(function(){
    waitForRep();
});
</script>