XML parse into dynamic column can be done with parse_xml(x).
Here is a workaround to enable translation of XMLs with namespaces.
datatable (dumpInput:string)
['<SOAP-ENV:Envelope xmlns:e="http://www.test.com"></SOAP-ENV:Envelope>']
| extend x = replace("<(.+?):", @"<\1", dumpInput)
| project s=parse_xml(x)
| extend s["SOAP-ENVEnvelope"]["@xmlns:e"]
