Aviation Knowledge Test
English Language Skills Test
CASS – CAE Aircrew Selection System
Group Exercise
Personal Interview
This is what is given on the website. So you can start doing research on the topics. Being at CPL level, they would probably expect you to know your CPL stuff in and out. English test shouldn't be a problem if you've managed to pass 10+2 level English. CASS, I wouldn't know, but some research on google might help. Then there is the group exercise and personal interview.
MKS