I've found it in Tk::Widget. So it should work when invoked on your object. If not, please post an example.

Update: Minimal example:

use Tk;
use strict;
use warnings;

my $mw = MainWindow->new;
$mw->Label(-text => 'Hello, world!')->pack;
$mw->Button(
            -text    => 'Quit',
            -command => sub { exit },
           )->pack;


my (@bindtags) = $mw->bindtags;
print "\$mw's bindtags:\n", join("\n", @bindtags), "\n";

print "\nCORRECTION: NOW THE bindDump():\n", $mw->bindDump();  # <-- U
+PDATE2

MainLoop;
[download]

mw's bindtags:
MainWindow
.
all

CORRECTION: NOW THE bindDump():

## Binding information for '.', MainWindow=HASH(0xf20e08) ##
1. Binding tag 'MainWindow' has no bindings.

2. Binding tag '.' has no bindings.

3. Binding tag 'all' has these bindings:
                     <Key-F10> : Tk::Callback=SCALAR(0xf57d08)        
+   
                                   'FirstMenu'
                     <Alt-Key> : Tk::Callback=ARRAY(0xf57c48)         
+   
                                   'TraverseToMenu'
                                     Tk::Ev=SCALAR(0xcb3258)          
+       : 'K'
                   <<LeftTab>> : Tk::Callback=SCALAR(0xf57ba0)        
+   
                                   'focusPrev'
                     <Key-Tab> : Tk::Callback=SCALAR(0xf57bb8)        
+   
                                   'focusNext'
[download]

No use Tk::Widget; required. That is done automatically.

Update2: Thanks to beech for pointing out that the real call to bindDump() was missing.