That code won't work as the server code is executed and the results sent to the browser to display, so you can't mix server code and client code. You'll need to do something like this;
<asp:TextBox ID="PFtxtname1" runat="server" Text="a"></asp:TextBox>
<asp:TextBox ID="PFtxtname2" runat="server" Text="b"></asp:TextBox>
<asp:TextBox ID="PFtxtname3" runat="server" Text="c"></asp:TextBox>
<asp:TextBox ID="PFtxtname4" runat="server" Text="d"></asp:TextBox>
<asp:TextBox ID="PFtxtname5" runat="server" Text="e"></asp:TextBox>
<asp:TextBox ID="PFtxtname6" runat="server" Text="f"></asp:TextBox>
<script type="text/javascript">
$(document).ready(function () {
$("input[id*='PFtxtname']").each(function () {
alert($(this).val());
});
});
</script>