Baserat på det här svaret
Borde vara så här:
declare
v_xml clob;
begin
v_xml := '<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<soap:Body>
<addResponse xmlns="http://tempuri.org/">
<addResult>20</addResult>
</addResponse>
</soap:Body>
</soap:Envelope>';
for c in (select results
from xmltable(xmlnamespaces(default 'http://tempuri.org/',
'http://schemas.xmlsoap.org/soap/envelope/' as
"soap" ),
'soap:Envelope/soap:Body/addResponse' passing
xmltype(v_xml) columns results varchar(100) path
'./addResult')) loop
dbms_output.put_line('the result of calculation is : ' || c.results);
end loop;
end;