protected void GridViewUserList_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        string Message;

        Message = "Вы уверены, что хотите удалить пользователя?";
        
        if (e.Row.RowType == DataControlRowType.DataRow)
        {
            // ссылка на Delete LinkButton
            ImageButton DelB = (ImageButton)e.Row.Cells[0].Controls[2];

            DelB.OnClientClick = string.Format("return confirm('" + Message + "');");
        }
    }

....

<asp:GridView ID="GridViewUserList" runat="server" AutoGenerateColumns="False" EnableModelValidation="True" 
                  BorderColor="Green" BorderStyle="Solid" AllowPaging="True" 
                  DataKeyNames="id" DataSourceID="SqlDataSource4" 
                  BorderWidth="5px" onrowdeleted="GridViewUserList_RowDeleted"
                                    onrowupdated="GridViewUserList_RowUpdated" 
                                    onrowdatabound="GridViewUserList_RowDataBound" >
        <Columns>
            <asp:CommandField ShowDeleteButton="True" ShowEditButton = "true" ButtonType="Image"
                              EditImageUrl="~/img/uedit.png" DeleteImageUrl="img/udelete.png" 
                              UpdateImageUrl="img/yes.png" CancelImageUrl="img/cancel.png" />
            <asp:BoundField HeaderText = "ID"               DataField = "id" SortExpression = "id" ReadOnly="True" InsertVisible="False" ></asp:BoundField>
            <asp:BoundField HeaderText = "ФИО"              DataField = "uname" SortExpression = "uname"></asp:BoundField>
            <asp:BoundField HeaderText = "Имя пользователя" DataField = "ulogin" SortExpression = "ulogin"></asp:BoundField>
            <asp:BoundField HeaderText = "Пароль"           DataField = "upasswd" SortExpression = "upasswd"></asp:BoundField>
            <asp:TemplateField HeaderText="Блокировка">
                <EditItemTemplate>
                    <asp:DropDownList ID="UserBlockDropDownList" runat="server" DataSourceID="SqlDataSource2" SelectedValue='<%# Bind("isblocked") %>' DataTextField="isblocked"></asp:DropDownList>
                </EditItemTemplate>
                <ItemTemplate>
                    <asp:Label ID="UserBlockLabel" runat="server" Text='<%# Bind("isblocked") %>'></asp:Label>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Роль">
                <EditItemTemplate>
                    <asp:DropDownList ID="UserRoleDropDownList" runat="server" DataSourceID="SqlDataSource5" SelectedValue='<%# Bind("urole") %>' DataTextField="Brief"></asp:DropDownList>
                </EditItemTemplate>
                <ItemTemplate>
                    <asp:Label ID="UserRoleLabel" runat="server" Text='<%# Bind("urole") %>'></asp:Label>
                </ItemTemplate>
            </asp:TemplateField>
        </Columns>
    </asp:GridView>

<asp:SqlDataSource ID="SqlDataSource4" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>" 
                       ProviderName="System.Data.SqlClient" SelectCommand = "trd_UserAction_Select" SelectCommandType = "StoredProcedure"
                                                            InsertCommand = "trd_UserAction_Insert" InsertCommandType = "StoredProcedure"
                                                            UpdateCommand = "trd_UserAction_Update" UpdateCommandType = "StoredProcedure"
                                                            DeleteCommand = "trd_UserAction_Delete" DeleteCommandType = "StoredProcedure"
                                                            OldValuesParameterFormatString = "original_{0}">
        <SelectParameters>
            <asp:ControlParameter ControlID="DropDownList1" DefaultValue="1" Name="isblocked" PropertyName="SelectedValue" Type="Int16" />
            <asp:ControlParameter ControlID="DropDownList2" DefaultValue="1" Name="crole" PropertyName="SelectedValue" Type="Int16" />
            <asp:ControlParameter ControlID="TextBox1" DefaultValue="%" Name="cname" PropertyName="Text" Type="String" />
        </SelectParameters>
        <InsertParameters>
            <asp:Parameter Type = "String" Name = "uname"></asp:Parameter>
            <asp:Parameter Type = "String" Name = "ulogin"></asp:Parameter>
            <asp:Parameter Type = "String" Name = "upasswd"></asp:Parameter>
            <asp:Parameter Type = "String" Name = "isblocked"></asp:Parameter>
            <asp:Parameter Type = "String" Name = "urole"></asp:Parameter>
        </InsertParameters>
        <UpdateParameters>
            <asp:Parameter Type = "Int16"  Name = "id"></asp:Parameter>
            <asp:Parameter Type = "String" Name = "uname"></asp:Parameter>
            <asp:Parameter Type = "String" Name = "ulogin"></asp:Parameter>
            <asp:Parameter Type = "String" Name = "upasswd"></asp:Parameter>
            <asp:Parameter Type = "String" Name = "isblocked"></asp:Parameter>
            <asp:Parameter Type = "String" Name = "urole"></asp:Parameter>
        </UpdateParameters>
        <DeleteParameters>
            <asp:Parameter Type = "Int16"  Name = "id"></asp:Parameter>
        </DeleteParameters>
    </asp:SqlDataSource>