You can use template field or any bount field and then us JS to display or hide textbox
<asp:gridview id="GridView1" runat="server" xmlns:asp="#unknown">
<columns>
<asp:templatefield>
<itemtemplate>
<asp:checkbox id="chk" runat="server" onclick="cknunck(this)" />
<asp:textbox id="tbx" runat="server" style="display:none;"></asp:textbox>
</itemtemplate>
</asp:templatefield>
</columns>
</asp:gridview>
function cknunck(ck)
{
var dis="none";
if(ck.checked)
dis="";
ck.nextSibling.style.display=dis;
}
you can use style.visibility="hidden" tag also in place of style.display
if this will help you then please mark as solution