hey satish.lx,
Welcome to the forums!
These are good questions that I don't 100% know the answers to but I'm going to take a random educated guess at them.
1. Is course and lab training is required for appearing in exam?
My guess would be yes simply due to the fact that the certification examination requires you to have an OSID and password. Not only that, but I don't think the off-sec guys would put at risk the possibility of having the final certification examination challenge exposed by someone willing to pay the $60.00 listed for the 'Certification Retake'. I could definitely be wrong though; I've never seen someone pass the Examination or Take it without being a PWB student.
2. Where to get this exam ? i meant any specific location of city ?
As far as I know, the examination is only offered online to students. The examination is not your casual written test. It is a hands-on prove your abilities type exam that takes place in a secluded environment which the off-sec folks give you credentials to VPN into. It is not tied directly to any specific location or city.
3. How much cost for certification?
You should take a look at the costs
here. I doubt they offer just an exam challenge attempt for a fee.
If you'd like official answers you may want to contact Offensive-Security through their
Contact Us Form or by PMing one of the mods in their IRC Channel. Last time I checked they're located on Freenode in channel #offsec
Cheers,
-kris