is the sentence correct? if not then how can it be corrected
"Not a word of HIndi they speak "!
Your sentence is not correct. You can correct it in several ways:
1) Not a word of Hindi do they speak. (correct but almost never said)
2) They speak not a word of Hindi. (better but still not commonly said)
3) They don't speak a word of Hindi. (best choice and usual way to say it)