Like this:

my %form;

my %field = (
    'key 1' => 'value 1',
    'key 2' => 'value 2',
);

$form{another_hash} = \%field;

for my $first_key ( keys %form ) {
    for my $hoh_keys ( keys %{ $form{$first_key} } ) {
        print $hoh_keys, $/;    ## get the keys
    }
}
[download]

You can also check perldsc. or ^**Specifically: Access and Printing of a HASH OF HASHES
You really can use Data::Dumper to see how the data structure looks like, then you can get at what you want.

use Data::Dumper;
...
print Dumper \%form;
[download]

produces..

$VAR1 = {
          'another_hash' => {
                              'key 2' => 'value 2',
                              'key 1' => 'value 1'
                            }
        };
[download]

** Updates.