<table id="table1" runat="server" style="position:absolute; left: 449px; top: 96px; z-index: 102;">
        <tr runat="server" id="trow1">
        <td id="tdata1" runat="server">
            <asp:TextBox ID="txtbox1" runat ="server" />
        </td>
        <td>
            <asp:DropDownList ID="ddlist1" runat="server" />
        </td>
        </tr>
        </table>
        <asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Style="z-index: 104;
            left: 464px; position: absolute; top: 278px" Text="Button" />

 protected void Page_Load(object sender, EventArgs e)
    {
       TextBox txt = new TextBox();
        DropDownList ddl = new DropDownList();
        HtmlTableRow row = new HtmlTableRow();
        HtmlTableCell cell =new HtmlTableCell();
        
            cell.Controls.Add(txt);
            txt.ID = "txtbox2";
            cell.Controls.Add(ddl);
            ddl.ID = "dropdown1";
            ddl.Items.Add("abcd");
            ddl.Items.Add("efgh");
            row.Cells.Add(cell);
                 
        table1.Rows.Add(row);
    }

protected void Button1_Click(object sender, EventArgs e)
    {
        string str = ((TextBox)table1.Rows[1].Cells[0].FindControl("txtbox2")).Text;
        string str1 = ((DropDownList)table1.Rows[1].Cells[0].FindControl("dropdown1")).SelectedValue;
        Response.Write(str + " " + str1);
    }