Are you using rules? In a repeating table, current() will either be pointing to your row or to the field, depending on how you have things set up.
I'm not sure whether my:Repeating is the actual repeating row or the container and my:ITR is the repeating row.
You can try one of the following (assumes current() = the row):
xdXDocument:GetDOM("Income")/dfs:myFields/dfs:dataFields/d:Income/@BAS_Related[../@Income_Item = current()/my:ITR/my:Label]
xdXDocument:GetDOM("Income")/dfs:myFields/dfs:dataFields/d:Income/@BAS_Related[../@Income_Item = current()/my:Label]
If those don't work, try one of these (assumes current() = the field):
xdXDocument:GetDOM("Income")/dfs:myFields/dfs:dataFields/d:Income/@BAS_Related[../@Income_Item = current()/../my:ITR/my:Label]
xdXDocument:GetDOM("Income")/dfs:myFields/dfs:dataFields/d:Income/@BAS_Related[../@Income_Item = current()/../my:Label]