var a = xmlhttp.responseXML.querySelector("response->certinfo->attestat->notary");
alert(a);
пишет null
xml такой
<?xml version="1.0" encoding="windows-1251"?>
<response retval="2">
<fullaccess></fullaccess>
<certinfo wmid="123456789">
<attestat>
<row tid="" recalled="" datecrt="123" regnickname="456" regwmid="789" status="100" notary="55"/>
...