*A* way.

use strictures;
use XML::LibXML;

my $dom = XML::LibXML
    ->load_xml({ IO => \*DATA });

my $last = [ $dom->findnodes("/library/book[last()]") ]->[0];
print $last->findvalue("title"), $/;

__DATA__
<library>
    <book>
      <title>Perl Best Practices</title>
      <src>Use python. But I keed!</src>
    </book>
    <book>
      <title>Perl Cookbook, Second Edition</title>
      <src>You would make more cooking meth. But I keed!</src>
    </book>
    <book>
      <title>Guitar for Dummies</title>
      <src>Stratocaster. Oh, I'm sorry, did I stutter?</src>
    </book>
</library>
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