$(function () {
        $.datepicker.regional[""].dateFormat = 'dd/mm/yy';
        $.datepicker.setDefaults($.datepicker.regional['it']);
    });

oTable = $('#dtElenco').dataTable({
                "oLanguage": {
                    "sUrl": "/Metronic/plugins/data-tables/language/it-IT.txt"
                },
                "aoColumns": [
                  { "bSortable": false },
                  { "bSortable": false },
                   null,
                    null,
                  null,                                    
                  null,
                  null,
                  null,                  
                  { "bSortable": false }
                ],
                "aaSorting": [[2, "desc"]],
                "aLengthMenu": [
                    [20, 50, 100],
                    [20, 50, 100] // change per page values here
                ],
                // set the initial value
                "iDisplayLength": 20,
                "sPaginationType": "bootstrap",                
                "aoColumnDefs": [
                    { 'bSortable': false, 'aTargets': [0] },
                    { "bSearchable": false, "aTargets": [0] }
                ],
                "bProcessing": true,
                "bServerSide": true,
                "sAjaxSource": "/Handler/ajaxTable.ashx",                
                "fnServerData": function (sSource, aoData, fnCallback) {
                    aoData.push({ "name": "type", "value": "centri" });
                    $.ajax({
                        "dataType": 'json',
                        "contentType": "application/json; charset=utf-8",
                        "type": "GET",
                        "url": sSource,
                        "data": aoData,
                        "success": function (msg) {                            
                            var json = jQuery.parseJSON(msg);
                            fnCallback(json);
                            $("#dtElenco").show();
                        },
                        error: function (xhr, textStatus, error) {
                            
                            if (typeof console == "object") {
                                console.log(xhr.status + "," + xhr.responseText + "," + textStatus + "," + error);
                            }
                        }
                    });
                },
            })
            .columnFilter({
                //sPlaceHolder: "head:before",
                "aoColumns": [
                                null,
                                null,
                                { "type": "date-range", sRangeFormat: "{from} {to}" },
                                { "type": "date-range", sRangeFormat: "{from} {to}" },
                                { "type": "text" },
                                { "type": "text" },
                                null,
                                { type: "select", values: ['ON', 'SB', 'ATTESA ATTIVAZIONE', 'OFF'] },
                                null
                            ]
            });

File .ashx

param1 = Convert.ToString(HttpContext.Current.Request["sSearch_2"]);
QUI RICEVO undefined~undefined