Hi, here is the basic idea. There is some error checking left out, like removing a key from the hash if you destroy a toplevel, but it shows the idea. This is a very straight forward method, but there are others, like looping thru all the pack children of the toplevel, then finding the Frame hash.... but stick with the straight forward until you get more experience.

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $count = 0;
my %tls;   #hash to store the toplevels

my $mw = MainWindow->new;
$mw->title( "MainWindow" );

my $spawn_button = $mw->Button( -text => "Toplevel", 
                -command => \&do_Toplevel )->pack();

my $report_button = $mw->Button( -text => "Report", 
                -command => \&report )->pack();


MainLoop;

sub do_Toplevel {
    
   my $num = $count++;
   $tls{$num}{'tl'} = $mw->Toplevel();
        
   $tls{$num}{'tl'}->protocol('WM_DELETE_WINDOW' => sub {
         print "do nothing here\n"; #prevents destruction of $tl
                            #by WM control
     });
        
  $tls{$num}{'tl'}->title( "Toplevel $count" );

  $tls{$num}{'frame'}= $tls{$num}{'tl'}->Frame()
              ->pack(-expand=>1, -fill=>'both');

  $tls{$num}{'label'} = $tls{$num}{'frame'}->Label(-text=>$count)
                        ->pack(-expand=>1, -fill=>'x');

  $tls{$num}{'tl'}->Button(
    -text    => "Close",
    -command => sub { $tls{$num}{'tl'}->withdraw; 
              }
        )->pack;
}

sub report {
 
  foreach my $num (keys %tls){
        
         print "toplevel $num has frame ", $tls{$num}{'frame'},"\n";
  
       }
}
[download]