Assuming gibsonca.xml looks like this:

<gibsonca>
<abc>fds </abc> <!-- ok -->
<ddd></ddd> <!-- not ok -->
<eee> </eee> <!-- not ok -->
</gibsonca>

The following program will print "3" and "4".

#!/opt/perl/bin/perl -T
use strict;
use warnings;
use Carp;
use English qw(-no_match_vars);
use Try::Tiny;
use XML::LibXML;

our $VERSION = '0.1';

my $file = 'gibsonca.xml';
my $dom;

open my $fh, '<', $file
    or carp "Can't open $file: $OS_ERROR";

try {
    $dom = XML::LibXML->load_xml(
        {   IO           => $fh,
            line_numbers => 1,
        }
    );
}
catch {
    print "Error parsing $file";
};

close $fh
    or carp "Can't close $file: $OS_ERROR";

for my $e ( $dom->findnodes('//*') ) {

    my $t = $e->textContent();
    $t =~ s{\A \s+ \z}{}xms;

    if ( !$t ) {
        print $e->line_number() . "\n";
    }
}

exit 0;
__END__