my $HoH = {
          'pk1' => {
                      'sk1'  => 'val1',
                      'sk2'  => 'val2,
                      'score'=> 47
                         },

          'pk2' => {
                      'sk1' => 'val3',
                      'sk2' => 'val4',
                      'score' => 14
                         },
          'pk3' => {
                      'sk1' => 'val5',
                      'sk2' => 'val6',
                      'score' => 64
                    }
        };

##</code><code>##

my @best_key = sort { keys %{$HoH{'score'}{$a}} <=> keys %{$HoH{'score'}{$b}}  } keys %HoH;