Hai irfan shaikh,

There's no diploma course available in law. 

If you really want to be a lawyer professionally, After 12th , you go for 5year integrated LLB. 

For more details,check this link:

https://dqxeclau.top/news/9564-law-entrance-tests

Some university offers diploma course in PG level. For this you must complete UG degree in any recognised board.

For reference :

http://tndalu.ac.in/distance_education_department.php

Hope it's useful for you! 

Thank you