use strict;
use XML::LibXML;

my $string = <<"";
<?xml version="1.0"?>
<ItemLookupResponse xmlns="http://webservices.amazon.com/AWSECommerceService/2013-08-01">
  <Items>
    <Item>
      <ASIN>B01KI4JSQY</ASIN>
    </Item>
  </Items>
</ItemLookupResponse>

my $doc = XML::LibXML->new->load_xml(string => $string, {no_blanks => 1});
my $xc = XML::LibXML::XPathContext->new($doc);
$xc->registerNs( x => $doc->getDocumentElement->namespaceURI );

for my $item ( $xc->findnodes('//x:ItemLookupResponse/x:Items/x:Item') )
{
        print $item->firstChild->nodeName, "\n";
        print $item->firstChild->toString, "\n";
        print $xc->findvalue('x:ASIN', $item), "\n";
}