You can add button and textbox in the following manner so that when click on button textbox will be shown:
<asp:content id="BodyContent" contentplaceholderid="MainContent" runat="server" xmlns:asp="#unknown">
<div class="jumbotron">
<asp:gridview autogeneratecolumns="false" id="gdv1" runat="server">
<columns>
<asp:boundfield datafield="ID" />
<asp:boundfield datafield="FirstName" />
<asp:boundfield datafield="LastName" />
<asp:templatefield>
<itemtemplate>
<input type="text" id="<%#Eval("ID") %>" hidden="hidden" />
</itemtemplate>
</asp:templatefield>
<asp:templatefield>
<itemtemplate>
<input type="button" value="show" onclick="Show(this)" />
</itemtemplate>
</asp:templatefield>
</columns>
</asp:gridview>
</div>
<script type="text/javascript">
function Show(e) {
$row = $(e).parent().siblings("").find('input');
$row.show();
}
</script>
</asp:content>