The best way to get this information is to use jbpm-bam module (basically it logs all the activities of your processes into a db) and to query NodeInstanceLog table.
This is a query you can use:
SELECT
n
FROM
NodeInstanceLog n
WHERE
n.processInstanceId = :processInstanceId and
n.nodeName != ''
GROUP BY n.nodeName
HAVING MOD(COUNT(n), 2) = 1