I found the solution
Protected Sub btnsave_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnsave.Click
con.Open()
Dim sql As String = "insert into t2 (idd,col1,col2) values ( @t1,@t2,@ddd)"
Dim cmd As New SqlCommand(Sql, con)
cmd.Parameters.AddWithValue("@t1", CType(Panel1.FindControl("TextBoxRow_" & ctr), TextBox).Text)
cmd.Parameters.AddWithValue("@t2", CType(Panel1.FindControl("TextBox2Row_" & ctr), TextBox).Text)
cmd.Parameters.AddWithValue("@ddd", CType(Panel1.FindControl("dd_" & ctr), DropDownList).Text)
Dim obj As Object = cmd.ExecuteNonQuery()
If IsDBNull(obj) Then
Response.Write("error, try agin")
Else
Response.Write("Done")
End If
End Sub