use 5.010;
use strict;
use warnings;
use XML::LibXML;

my $parser = XML::LibXML->new();
my $doc = $parser->parse_string(<<"EOM")->documentElement;
<threads>
  <thread>
    <date>11.22.3333</date>
    <name>Max Mustermann</name>
  </thread>
</threads>
EOM

sub walk {
    my ($node, $stack) = @_;
    my @children = $node->findnodes("*");
    for my $child (@children) {
        if (ref ($child) eq "XML::LibXML::Element") {
            walk($child, [@$stack, $node->nodeName])
        }
    }
    unless (@children) {
        say join "/", @$stack, $node->nodeName
    }
}
walk($doc, []);