Hi Balram,
A blog post from SAP Community has a good set of examples - here is a link to one of our posts from last year: handy CABI Query Builder example queries
Here's an example he lists to obtain a list of all reports and documents those are in public folders including Sub folders. (Excluding instances, personal documents and inbox documents)
SELECT * FROM CI_INFOOBJECTS WHERE SI_KIND IN ('FullClient', 'Txt', 'Excel', 'Webi', 'Analysis', 'Pdf', 'Word', 'Rtf', 'CrystalReport', 'Agnostic') AND SI_RUNNABLE_OBJECT = 0 AND SI_INSTANCE_OBJECT = 0 AND SI_ANCESTOR = 23
_R