use strict;
use warnings;
use XML::LibXML;

my $file = $ARGV[0];

my $parser = XML::LibXML->new();
my $doc    = $parser->parse_file($file);
my $root   = $doc->documentElement();

for my $w_node (
    $root->findnodes('/e/p//w')
) {
    my ($wn_anchor) = $w_node->findnodes('a[@name="wn"]') or next;
    my ($l_anchor)  = $w_node->findnodes('a[@name="l"]' ) or next;

    ...
}