En kombination av replace , extract och och xpath-uttryck skulle kunna göra:
select
replace(replace(
extract(
xmltype (q'{<?xml version="1.0" encoding="utf-8"?>
<!--ADOR Acknowledgement 2-->
<AckTransmission xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.irs.gov/efile">
<TransmissionHeader recordCount="1">
<Jurisdiction>ALABAMA</Jurisdiction>
<TransmissionId>1946157056</TransmissionId>
<Timestamp>2012-08-16T01:25:47-05:00</Timestamp>
<Transmitter>
<ETIN>00000</ETIN>
</Transmitter>
<ProcessType>T</ProcessType>
<AgentIdentifier>ACK</AgentIdentifier>
</TransmissionHeader>
<Acknowledgement>
<SubmissionId>X1684956672</SubmissionId>
<EFIN>X16849</EFIN>
<GovernmentCode>ALST</GovernmentCode>
<SubmissionType>XMLTOM</SubmissionType>
<TaxYear>9999</TaxYear>
<SubmissionCategory>MFET</SubmissionCategory>
<AcceptanceStatus>A</AcceptanceStatus>
<ContainedAlerts>0</ContainedAlerts>
<StatusDate>2012-08-16</StatusDate>
</Acknowledgement>
</AckTransmission>}'),
'/descendant::comment()'
), '<!--'), '-->') as comment_
from dual;