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

    'pk2' => 
    {
        'sk1'   => 'val3',
        'sk2'   => 'val4',
        'score' => 14
    },

    'pk3' => 
    {
        'sk1'   => 'val5',
        'sk2'   => 'val6',
        'score' => 64
    }
};
        
my @keys = sort { $HoH->{$a}->{score} <=> $HoH->{$b}->{score} } keys %{$HoH};
print "@keys";