1. Create a DEBUG logger for org.apache.jackrabbit.oak.query
2. tail that log
3. run your query builder query above and see what gets logged. It will log both the xpath and jcr-sql equivalent
select [jcr:path], [jcr:score], * from [cq:Page] as a where contains(*, 'mysearchKeyword') and isdescendantnode(a, '/content/mywebsite/dashboard) union select [jcr:path], [jcr:score], * from [cq:Page] as a where contains(*, 'mysearchKeyword') and isdescendantnode(a, '/content/dam/mywebsite') union select [jcr:path], [jcr:score], * from [dam:Asset] as a where contains(*, 'mysearchKeyword') and isdescendantnode(a, '/content/mywebsite/dashboard') union select [jcr:path], [jcr:score], * from [dam:Asset] as a where contains(*, 'mysearchKeyword') and isdescendantnode(a, '/content/dam')