You need to catch a cab or self drive to Pondicherry from chennai airport. There are buses from Koyambedu to Pindichery. So from airport take a cab to Koyambedu main bus stop and there you will get a bus.
Going to ldakh trip if you are interested I will pay all expenses and trip expense so don't worry money if you interested then ping me on whatsapp =9057945121