how to ignore namespaces with XPath

You can do the same In XPath2.0 in a less verbose syntax:

/path/to/*:somenode

You can use the local-name() XPath function. Instead of selecting a node like

/path/to/x:somenode

you can select all nodes and filter for the one with the correct local name:

/path/to/*[local-name() = 'somenode']

Or you can use name():

/path/to/*[name() = 'somenode']

Or only search attributes:

//*[@attribute="this one"]

If you open the xml as a powershell object, it ignores the namespaces:

[xml]$xml = get-content file.xml
$xml.path.to.somenode