....

my ($score, $guess, $num1, $num2, $answer, $question); # added $question

....

#question widget
$mw->Label(-textvariable => \$question)->pack(-side => 'right'); # changed -text to -textvariable
# button to submit answer
$mw->Button(-text => 'Check me', -command => sub { checkanswer(); } )->pack(-side => 'right');

# add you score display stuff too

....

sub question {
    $table = $scale;
    $num1 = int(rand($table)+1);
    $num2 = int(rand(12)+1);
    $answer = $num1*$num2;
    $question = "$num1 x $num2 = ";
}

sub checkanswer {
  if ($answer == $guess) {
    $score++
  }else{
    $score--
  }

  # update score display here

  question(); # <-- generate a new question
}