Link button Click event not firing

<asp:Panel ID="pnlPopupQuestionAdd" runat="server">
                <div align="center" style="background-color: White; margin: 5px; padding: 5px;">
                    <table>
                        <tr>
                            <td colspan="2" align="center">
                                <asp:Label ID="lblHeader" runat="server" Text="Add Checklist Question" />
                            </td>
                        </tr>
                        <tr>
                            <td>
                                <asp:Label ID="lblPopFileType" runat="server" Text="Type:" />
                                <asp:Label ID="lblMandatoryFldType" runat="server" Text="*" ForeColor="Red" />
                            </td>
                            <td>
                                <asp:DropDownList ID="ddlPopupType" runat="server" />
                            </td>
                        </tr>
                        <tr>
                            <td>
                                <asp:Label ID="lblpopSchoolName" runat="server" Text="School Name:" />
                                <asp:Label ID="lblMandatoryFldName" runat="server" Text="*" ForeColor="Red" />
                            </td>
                            <td>
                                <asp:DropDownList ID="ddlPopSchoolName" runat="server" />
                            </td>
                        </tr>
                        <tr>
                            <td>
                                <asp:Label ID="lblPageNo" runat="server" Text="Page Number:" />
                            </td>
                            <td>
                                <asp:TextBox ID="txtPageNo" runat="server" />
                            </td>
                        </tr>
                        <tr>
                            <td>
                                <asp:Label ID="lblQuesNo" runat="server" Text="Question Number:" />
                                <asp:Label ID="lblMandatoryFldQuesNo" runat="server" Text="*" ForeColor="Red" />
                            </td>
                            <td>
                                <asp:TextBox ID="txtQuesNo" runat="server" />
                            </td>
                        </tr>
                        <tr>
                            <td>
                                <asp:RequiredFieldValidator ID="reqFldValQuesNo" runat="server" SetFocusOnError="true"
                                    ErrorMessage="Enter Question Number" ControlToValidate="txtQuesNo" />
                            </td>
                            <td>
                                <asp:RegularExpressionValidator ID="regExpValQuesNo" runat="server" ErrorMessage="Enter Numeric Only"
                                    SetFocusOnError="true" ControlToValidate="txtQuesNo" ValidationExpression="^\d+$" />
                            </td>
                            <td>
                            </td>
                        </tr>
                        <tr>
                            <td>
                                <asp:Label ID="lblQues" runat="server" Text="Checklist Question:" />
                                <asp:Label ID="lblMandatoryFldQues" runat="server" Text="*" ForeColor="Red" />
                            </td>
                            <td>
                                <asp:TextBox ID="txtQues" runat="server" TextMode="MultiLine" />
                            </td>
                        </tr>
                        <td></td>
                        <td>
                        <asp:RequiredFieldValidator ID="reqFldValAddQuesText" runat="server" ErrorMessage="Enter Question" SetFocusOnError="true" ControlToValidate="txtQues" />
                        </td>
                        <tr>
                            <td align="center" colspan="2">
                                <asp:Button ID="btnSave" runat="server" Text="Save" OnClick="btnSave_Click" />
                                <asp:Button ID="btnCancel" runat="server" Text="Cancel" OnClick="btnCancel_Click" />
                            </td>
                        </tr>
                        <tr>
                            <td colspan="2">
                                <asp:Label ID="lblNotes" runat="server" Text="Note: Question Number will overwrite Page Number in case of any discrepancies." />
                            </td>
                        </tr>
                    </table>
                </div>
            </asp:Panel>

<ajaxToolkit:ModalPopupExtender ID="popAddQues" runat="server" TargetControlID="lnkAddNewQues"
          PopupControlID="pnlPopupQuestionAdd" CancelControlID="btnCancel" Enabled="true"
          BackgroundCssClass="modalBackground" DropShadow="false" />

//link Button(on click Popup should come)
<asp:LinkButton ID="lnkAddNewQues" runat="server" Text="Add" OnClick="lnkAddNewQues_Click" />

protected void lnkAddNewQues_Click(object sender, EventArgs e)
       {
           fillType(ddlEditQuesType);
           fillSchool(ddlQuesEditSchoolName);
           ddlEditQuesType.SelectedItem.Text = ddlType.SelectedItem.Text;
           ddlQuesEditSchoolName.SelectedItem.Text = ddlSchoolName.SelectedItem.Text;
           //txtQuesEditPageNo,txtQuesEditQuesNo,txtChklistQuesEditQues
           string Ques = ddlChecklistQuestions.SelectedItem.Text;
           int length = Ques.Length;
           txtQuesEditPageNo.Text = Ques.Substring(0, 1);
           txtQuesEditQuesNo.Text = Ques.Substring(2, 1);
           txtChklistQuesEditQues.Text = Ques.Substring(4, length - 4);
       }