my $gene_to_find = 'NP_012';
my @matching_taxons;
for my $taxon (keys %gg) {
    for my $gene ( @{ $gg{$taxon} } ) {
        if ($gene eq $gene_to_find) {
            push @matching_taxons, $taxon;
        }
    }
}

if (@matching_taxons) {
   print("Gene $gene_to_find found in taxons @matching_taxons.\n");
} else {
   print("Gene $gene_to_find not found in any taxon.\n");
}