Questions about "sequence of tenses" often come up, here, because, for one thing, English appears to be changing in this regard. It makes it especially difficult to deal with, since native speakers do not necessarily agree about what is grammatical English. Being a rather old person, I speak a conservative version of English which generally requires sequence of tenses to be followed. For your example, "I knew you are a kind man", I would have to say, instead, "I knew you were a kind man". Personally, I allow present tenses embedded in the complements of past tense verbs only in the case of truisms in indirect discourse: "Henrietta emphasized that the earth still revolves about the Sun."
I have a theory about recent, more liberal dialects, and that is this: Apparent sequence of tense violations are permissible when the main verb can be interpreted as a parenthetical expression which somehow qualifies the assertion made by the complement sentence. Specifically, for your first example, I think "I knew you are a kind man" is okay, in recent English, because it is interpreted to mean "You are a kind man, as I knew." That is, the assertion made is "You are a kind man", and the "I knew" part is just a qualifier -- a sort of adverb.
So then, for your second example,
I knew you are reading a book now"
my prediction for neo-English, is that this will be grammatical if and to the extent that it can be interpreted to mean "You are reading a book now, as I knew." It's a task for the imagination to figure out the situation in which you would say such a thing, but if you can do that, your example sentence should sound okay.