"Він не може жити без віри."

Both "cannot" and "can not" are acceptable spellings, but the first is much more usual. http://www.oxforddictionaries.com/words/cannot-or-can-not

Radoslav123 is correct: "cannot" is one word, not two.

In this sentence "can" "not" should be written together, without a space - "cannot". The form with a space should be only used when you want to emphasize the inabilty to do something, e.g.: He can do it and I can not.

Приймайте "cannot"!