Show Hide Panel control inside GridView Row on Button Click in ASP.Net

Here I have created sample that full-fill your requirement.

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 ShowPanel(btnShow) {
            var row = $(btnShow).closest("tr");
             $(row).find('[id*=lblId]').html($("td", row).eq(0).html());
             $(row).find('[id*=lblName]').html($("td", row).eq(1).html());
             $(row).find('[id*=lblCountry]').html($("td", row).eq(2).html());
             $(row).find('[id*=pnlPopup]').show();
             $(btnShow).hide();
             return false;
        };

        function ClosePanel(btnClose) {
            var row = $(btnClose).closest("tr");
            $(row).find('[id*=pnlPopup]').hide();
            $(row).find('[id*=btnShow]').show();
            return false;
        }
    </script>
    <asp:GridView ID="GridView1" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White"
        runat="server" AutoGenerateColumns="false">
        <Columns>
            <asp:BoundField DataField="Id" HeaderText="Id" ItemStyle-Width="30" />
            <asp:BoundField DataField="Name" HeaderText="Name" ItemStyle-Width="150" />
            <asp:BoundField DataField="Country" HeaderText="Country" ItemStyle-Width="150" />
            <asp:TemplateField>
                <ItemTemplate>
                    <asp:Button ID="btnShow" Text="Show Data" runat="server" OnClientClick="return ShowPanel(this)" />
                    <br />
                    <asp:Panel ID="pnlPopup" runat="server" CssClass="modalPopup" Style="display: none">
                        <div class="header">
                            Details
                        </div>
                        <div class="body">
                            <table border="0" cellpadding="0" cellspacing="0">
                                <tr>
                                    <td style="width: 60px">
                                        <b>Id: </b>
                                    </td>
                                    <td>
                                        <asp:Label ID="lblId" runat="server" />
                                    </td>
                                </tr>
                                <tr>
                                    <td>
                                        <b>Name: </b>
                                    </td>
                                    <td>
                                        <asp:Label ID="lblName" runat="server" />
                                    </td>
                                </tr>
                                <tr>
                                    <td>
                                        <b>Country: </b>
                                    </td>
                                    <td>
                                        <asp:Label ID="lblCountry" runat="server" />
                                    </td>
                                </tr>
                            </table>
                        </div>
                        <div class="footer" align="right">
                            <asp:Button ID="btnClose" runat="server" Text="Close" CssClass="button" OnClientClick="return ClosePanel(this)" />
                        </div>
                    </asp:Panel>
                </ItemTemplate>
            </asp:TemplateField>
        </Columns>
    </asp:GridView>
    <asp:LinkButton Text="" ID="lnkFake" runat="server" />
</div>

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[3] { new DataColumn("Id"), new DataColumn("Name"), new DataColumn("Country") });
        dt.Rows.Add(1, "John Hammond", "United States");
        dt.Rows.Add(2, "Mudassar Khan", "India");
        dt.Rows.Add(3, "Suzanne Mathews", "France");
        dt.Rows.Add(4, "Robert Schidner", "Russia");
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }
}

Screenshot