<telerik:RadScriptManager ID="RadScriptManager1" runat="server">

                <CdnSettings TelerikCdn="Enabled" CombinedResource="Enabled"></CdnSettings>
                <Scripts>
                    <telerik:RadScriptReference Assembly="Telerik.Web.UI" Name="Telerik.Web.UI.Common.Core.js" />
                    <telerik:RadScriptReference Assembly="Telerik.Web.UI" Name="Telerik.Web.UI.Common.jQuery.js" />
                    <telerik:RadScriptReference Assembly="Telerik.Web.UI" Name="Telerik.Web.UI.Common.jQueryInclude.js" />
                </Scripts>
            </telerik:RadScriptManager>

            <script>
                function pageLoad() {
                    var grid = $find("<%=RadGrid1.ClientID%>");
                    alert(grid._showFilterMenu);
                }
            </script>


            <telerik:RadGrid ID="RadGrid1" runat="server" AllowPaging="True" Width="800px" OnNeedDataSource="RadGrid1_NeedDataSource">
                <MasterTableView AutoGenerateColumns="False" DataKeyNames="OrderID">
                    <Columns>
                        <telerik:GridBoundColumn DataField="OrderID" DataType="System.Int32"
                            FilterControlAltText="Filter OrderID column" HeaderText="OrderID"
                            ReadOnly="True" SortExpression="OrderID" UniqueName="OrderID">
                        </telerik:GridBoundColumn>
                        <telerik:GridDateTimeColumn DataField="OrderDate" DataType="System.DateTime"
                            FilterControlAltText="Filter OrderDate column" HeaderText="OrderDate"
                            SortExpression="OrderDate" UniqueName="OrderDate">
                        </telerik:GridDateTimeColumn>
                        <telerik:GridNumericColumn DataField="Freight" DataType="System.Decimal"
                            FilterControlAltText="Filter Freight column" HeaderText="Freight"
                            SortExpression="Freight" UniqueName="Freight">
                        </telerik:GridNumericColumn>
                        <telerik:GridBoundColumn DataField="ShipName"
                            FilterControlAltText="Filter ShipName column" HeaderText="ShipName"
                            SortExpression="ShipName" UniqueName="ShipName">
                        </telerik:GridBoundColumn>
                        <telerik:GridBoundColumn DataField="ShipCountry"
                            FilterControlAltText="Filter ShipCountry column" HeaderText="ShipCountry"
                            SortExpression="ShipCountry" UniqueName="ShipCountry">
                        </telerik:GridBoundColumn>
                    </Columns>
                </MasterTableView>
            </telerik:RadGrid>