use warnings;
use strict;
use List::MoreUtils qw(any);

my %hoa = (
    x => [ qw(a b c d) ],
    y => [ qw(e f g) ],
    z => [ qw(h i c j) ],
);

my $x = 'c';

for my $k (keys %hoa) {
    print "key $k has $x\n" if any { $_ eq $x } @{ $hoa{$k} };
}

__END__

key x has c
key z has c