What do you want to do? If you just need a simple socket connection listening, you don't need to fork, just use a fileevent to read the socket. Although fileevent may be unreliable on Windows, it often works.

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

$|=1;
$SIG{PIPE} = 'IGNORE';

my $listen = IO::Socket::INET->new(
    Proto       => 'tcp',
    LocalPort   => 7070,
    Listen      => 1,
    Reuse       => 1,
) or die "Can't create listen socket : $!\n";

my $mw = MainWindow->new();

my $text = $mw->Scrolled('Text',
                  -background =>'black',
          -foreground => 'yellow',
             )->pack();      

my $subframe = $mw->Frame()->pack();

$subframe->Button(-text => 'Clear',
         -command => sub {
                  $text->delete('1.0','end');
           })->pack(-side=>'left');

$subframe->Button(-text => 'Save Log',
         -command => sub {   })->pack(-side=>'left');

$subframe->Button(-text => 'Exit',
         -command => sub { exit  })->pack(-side=>'right');
                           
                           
$mw->fileevent($listen, 'readable', sub { new_connection($listen) });

Tk::MainLoop;

sub new_connection {
    my ($listen) = @_;
    my $client = $listen->accept() or warn "Can't accept connection";
    $client->autoflush(1);
    $mw->fileevent($client, 'readable', sub { handle_connection($clien
+t) });
    #$client->print("Connected\n");
    $text->insert('end', "Connected\t");
    $text->see('end');
}

sub handle_connection {
    my ($client) = @_;
    my $message = <$client>;
    if (defined $message and $message !~ /^quit/) {
     $message =~ s/[\r\n]+$//;
     #$client->print("Got message [$message]\n"); #echo back if wanted
     $text->insert('end', "Got message [$message]\t");
     $text->see('end');
    }
    else {
       $text->insert('end', "Connection Closed\n");
       $text->see('end');
       $client->close();
    }
}
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With the following minimal modifications to your code, it works.

I wouldn't advise using it as is particularly but if you can understand how the modifications make it work, you'll probably see a better way for doing this. (Hint: You won't need fork)

use strict;
use warnings;
use IO::Socket;
use threads;
use threads::shared;
use Thread::Queue;
use Tk;
$| = 1;


my $Q = new Thread::Queue; $Q->enqueue( 'Primer' );

my $server = IO::Socket::INET->new(
    LocalPort => 2345,
    Type      => SOCK_STREAM,
    Reuse     => 1,
    Listen    => 10
  )
  or die "Error: $@\n";

$SIG{CHLD} = sub { exit };
my $entry = "start...";
my $wsk   = \$entry;
my $main  = MainWindow->new( -title => 'Socket - listen', );
my $ent1  = $main->Label(
    -text => "I'm waitin on port 2345\n So, you tell me...",
)->pack();
my $ent2 = $main->Label(
    -text => $entry,
)->pack();
$main->repeat(
    100, sub{
        return unless $Q->pending;
        my $in = $Q->dequeue();
        $ent2->configure( -text => $in );
    }
);

my $child;
my $guzik1 = $main->Button(
    -text    => 'Exit',
    -command => sub { kill 9, $child; exit 0 },
)->pack( -side => 'bottom', );

$child = fork();
if ( $child == 0 ) {
    while ( my $client = $server->accept() ) {
        while ( defined( my $in = <$client> ) ) {
            #print $in;    #control
            $Q->enqueue( $in );
        }
    }
}

MainLoop()
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