Try setting the screen option. On my system, the default would be :0. 
#!/usr/bin/perl 

use strict;
use warnings;
use 5.012;
use Tk;
use Tk::DialogBox;

my $mw = MainWindow->new(-screen => $ARGV[0] || $ENV{'DISPLAY'});
$mw->geometry('200x200+-300+300');  
$mw->DialogBox(-buttons => [ 'OK' ])
->Show(-popover => $mw);

MainLoop;

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In reply to Re: Tk multiple monitor problem by Khen1950fx
in thread Tk multiple monitor problem by JohnRS

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