Handle CheckBox Check Uncheck event in multiple Nested Child GridView in ASP.Net

Here I have created sample that will help you out.

I referred below article

Collapsible Nested GridView with Paging using ASP.Net

HTML

<div>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script type="text/javascript">
    $(function () {
        $("[src*=minus]").each(function () {
            $(this).closest("tr").after("<tr><td></td><td colspan = '999'>" + $(this).next().html() + "</td></tr>");
            $(this).next().remove()
        });
    });
</script>
<asp:GridView ID="gvCustomers" runat="server" AutoGenerateColumns="false" CssClass="Grid"
    DataKeyNames="CustomerID">
    <Columns>
        <asp:TemplateField>
            <ItemTemplate>
                <asp:ImageButton ID="imgShow" runat="server" OnClick="Show_Hide_ChildGrid" ImageUrl="~/images/plus.png"
                    CommandArgument="Show" />
                <asp:Panel ID="pnlOrders" runat="server" Visible="false" Style="position: relative">
                    <asp:GridView ID="gvOrders" runat="server" AutoGenerateColumns="false" PageSize="5"
                        AllowPaging="true" OnPageIndexChanging="OnChildGrid_PageIndexChanging" CssClass="ChildGrid">
                        <Columns>
                            <asp:BoundField ItemStyle-Width="150px" DataField="OrderId" HeaderText="Order Id" />
                            <asp:BoundField ItemStyle-Width="150px" DataField="OrderDate" HeaderText="Date" />
                            <asp:TemplateField ItemStyle-Width="18%" HeaderText="I">
                                <ItemTemplate>
                                    <asp:TextBox ID="tb1I" OnTextChanged="OnChildTextChanged" runat="server" Width="100%"
                                        Style="text-align: left" Text='<%# Eval("ShippedDate","{0:dd/MM/yyyy}")%>' AutoPostBack="true"></asp:TextBox>
                                </ItemTemplate>
                                <ItemStyle Width="18%" />
                            </asp:TemplateField>
                            <asp:TemplateField Visible="true" ShowHeader="true" HeaderText="CHoose" ItemStyle-HorizontalAlign="Center">
                                <ItemTemplate>
                                    <asp:CheckBox ID="chkChoose" AutoPostBack="true" runat="server" OnCheckedChanged="OnChildCheckedChanged" />
                                </ItemTemplate>
                                <ItemStyle HorizontalAlign="Center" />
                            </asp:TemplateField>
                        </Columns>
                    </asp:GridView>
                </asp:Panel>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:BoundField ItemStyle-Width="150px" DataField="ContactName" HeaderText="Contact Name" />
        <asp:BoundField ItemStyle-Width="150px" DataField="City" HeaderText="City" />
    </Columns>
</asp:GridView>
</div>

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        gvCustomers.DataSource = GetData("select top 10 * from Customers");
        gvCustomers.DataBind();
    }
}

private static DataTable GetData(string query)
{
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand())
        {
            cmd.CommandText = query;
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.Connection = con;
                sda.SelectCommand = cmd;
                using (DataSet ds = new DataSet())
                {
                    DataTable dt = new DataTable();
                    sda.Fill(dt);
                    return dt;
                }
            }
        }
    }
}

protected void Show_Hide_ChildGrid(object sender, EventArgs e)
{
    ImageButton imgShowHide = (sender as ImageButton);
    GridViewRow row = (imgShowHide.NamingContainer as GridViewRow);
    if (imgShowHide.CommandArgument == "Show")
    {
        row.FindControl("pnlOrders").Visible = true;
        imgShowHide.CommandArgument = "Hide";
        imgShowHide.ImageUrl = "~/images/minus.png";
        string customerId = gvCustomers.DataKeys[row.RowIndex].Value.ToString();
        GridView gvOrders = row.FindControl("gvOrders") as GridView; gvOrders.ToolTip = customerId;
        gvOrders.DataSource = GetData(string.Format("select * from Orders where CustomerId='{0}'", customerId));
        gvOrders.DataBind();
    }
    else
    {
        row.FindControl("pnlOrders").Visible = false;
        imgShowHide.CommandArgument = "Show";
        imgShowHide.ImageUrl = "~/images/plus.png";
    }
}

private void BindOrders(string customerId, GridView gvOrders)
{
    gvOrders.ToolTip = customerId;
    gvOrders.DataSource = GetData(string.Format("select * from Orders where CustomerId='{0}'", customerId));
    gvOrders.DataBind();
}

protected void OnChildGrid_PageIndexChanging(object sender, GridViewPageEventArgs e)
{
    GridView gvOrders = (sender as GridView);
    gvOrders.PageIndex = e.NewPageIndex;
    BindOrders(gvOrders.ToolTip, gvOrders);
}

protected void OnChildCheckedChanged(object sender, EventArgs e)
{
    CheckBox cb = sender as CheckBox;
    if (cb.Checked)
    {
    }
}

protected void OnChildTextChanged(object sender, EventArgs e)
{
    TextBox tb = sender as TextBox;
    string txt = tb.Text;
}

Screenshot