I want to know whether I should go for EJB 2.0 or 3.0.
If you look at Sun's certification homepage, you'll see that there is no exam for EJB2.x.
do you need to know EJB 2.0 before you get started with 3.0?
No
Is there any book for SCBCD from Kathy seirra and Bert Bates?
No. Check other ranchers' threads (many people asking about books), and the
SCBCD Links.