There are several GnuCash XML examples available at https://nomina.bitplan.com.
To test locally you can run
nomina -l -s -i nomina_examples/expenses_xml.gnucash
expenses_xml.gnucash (GC-XML) 2014-01-02-2014-01-02 5 accounts, 2 transactions
Please note that nomina itself does not have a lot of features to work with your personal finance managament content yet. You might want to use the # Issue 7 - command line conversion support✓ and start a discussion or issue to have your own needs covered.