Whats the dominant ethnic group in India?

Indians. :)

no one, every village in india is different, the language changes, if slighty every 20 miles or so thats why english is used as it is the only language the whole country has been exposed to.

Whats the dominant ethnic group in India?

Answer to this question requires an understanding at three stages:
a) Who is dominant in the Indian country side?
It is mostly kshatriyas and brahmins.

Also Kshatriyas of India are indegenous people (as are Brahmins) as genetic and anthropoligical research has shown. You can read it here:
http://hindurajput.blogspot.com/#Origins_and_Geographical_Presence

b) Who is dominant in Indian metros?
It is mostly the trading class like khatris, marwaris, Baniyas, Gujjus etc.

c) Who is dominant politically?
It is mostly groups who have the largest population. This is why there is strong surge in parties which represent the schedule castes.

-Digvijay