Learn to read the perldocs. From "perldoc Tk::Dialog"

The actual Dialog is shown using the Popup method. Any other options s
+upplied to Show are passed to Popup, and can be used to  position the
+ Dialog on the screen. Please read Tk::Popup for  details.
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Example:

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

my $mw = MainWindow->new();
$mw->geometry("600x400+100+100");

my $dialog = $mw->DialogBox(
         -title => 'Test',
      -buttons => [qw/Yes No Cancel/], 
      );

my $lifter;

$mw->Button(-text=>'Get_dialog',
            -command => sub{
             $lifter = $mw->repeat(100,sub{ $dialog->raise });

        #my $answer = $dialog->Show;
            my $answer = $dialog->Show(-popover => $mw);

        $lifter->cancel;
        #do your $dialog return testing 

        }

  )->pack;
MainLoop;
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Note, this may not work on old versions of Tk, like Tk800 on Perl5.6, but show some code and give more details if you still have a problem.