As the Anonymous Monk said, there isn't a way of cloning a widget.  However, you can achieve similar functionality by just creating a subroutine to handle the details of the widget you wish to "duplicate".

For example, here's a short program that creates two nearly identical buttons, each on a separate page of a 2-page NoteBook:

#!/usr/bin/perl -w

use strict;
use warnings;

use Tk;
use Tk::NoteBook;


# Main program
my $mw  = new MainWindow(-title => 'Duplicated widget example');
my $nb  = $mw->NoteBook()->pack();
my $pg1 = $nb->add("Page 1", -label => "Page 1");
my $pg2 = $nb->add("Page 2", -label => "Page 2");

my $bu1 = add_button($pg1, "Press Me", "I'm a button on Page 1");
my $bu2 = add_button($pg2, "Press Me", "I'm a button on Page 2");
MainLoop;


# Subroutines
sub add_button {
    my ($page, $label, $output) = @_;

    # These attributes will be common to the button
    my $bg     = 'hotpink';
    my $width  = 20;
    my $height = 5;
    my $font   = 'Helvetica 20';

    # What happens when the button is pressed?
    my $psub = sub {
        print "$output\n";
    };

    # Create the Button widget and pack it
    my $btn = $page->Button(-bg => $bg, -text => $label);
    $btn->configure(-font => $font, -width => $width, -height => $heig
+ht);
    $btn->configure(-command => sub { $psub->() });
    $btn->pack();
    return $btn;
}
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The subroutine add_button handles the details of the button you wish to duplicate.  When you call add_button, it adds a button to the specified page of the NoteBook ($1) with the given label ($2) and output text ($3).

Any other attribute of the button (ie. anything not passed as a subroutine argument) will be the same for each button created.  In the example I've given you, the color, font, and size (height and width) are all constant for any button created with the subroutine.