XPath for elements with attribute not equal or does not exist

Answer 1

The "hard part" is actually easy: A basic

element[not(@attribute= 'value')]

predicate will exclude elements without the attribute and elements for which attribute equals value.

So, in your specific case, all row elements that do not have @SubID equal to 1:

/test/table/rows/row[not(@SubID = '1')]

selects

<row ID="1" Name="A"/>
<row ID="3" Name="C"/>
<row ID="5" Name="E"/>
<row ID="4" Name="E" SubID="2"/>

as requested.