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I just made an attempt to recall a case when I could possibly use this word, and guess what?
It's either my memory fails me or the word is really very rare.
While it can be found sometimes in...

No, you can't.

каков is very rare and limited mostly to an archaic or bookish style, it is used to ask what smt is like. You might go through life and never have to use this word or bump into it....