你是不是漏了个n。原句应该是:There are known knowns。详见维基百科https://en.wikipedia.org/wiki/There_are_known_knowns。
原文摘要:“Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns—the ones we don't know we don't know. And if one looks throughout the history of our country and other free countries, it is the latter category that tends to be the difficult ones.”
即there are known knowns = there are things we know we know
are 动词
known 形容词
knowns 名词复数