Hi Chandrasekhar,
I'd say that one should have a good understanding of EJB-QL prior to taking the exam.
The best way to do it is to read the theory and
write the actual EJB-QL for your test ejb app and test that it works as expected.

Alex (SCJP 1.4, SCBCD 1.3, SCWCD 1.4, SCJD 1.4)