>>>>>Ah, two things here. First, the lack of word for "what" instead of "what" in English, the first one asking for an adjective ("what door is this" - "a green one"), the latter one for definition ("what do we have here?", "a door"). I've seen this so many times...
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>>If we wanted to know that we'd say "What colour door is this?"
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>A guy tries something (a car, suit, dish, anything). The other guy wants to know the verdict and asks: "kakvo je" (cf. Russian какой), a "what's it like" but not really asking for a comparison ("it's like a hedgehog"), but rather asking for some quality ("it's good", "it's a bit rusty", "tasted like ratburger"), and definitely not asking a "what is it", because they both know what it is.
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>Another example... person A knows person C, while B does not, so, B asks A about C, "kakav je C?" - "{missing word here} is C?". Possible answers include "incompetent", "illiterate", "funny", "good looking", "yellow bellied" etc. Wrong answers: "idiot", "engineer", "humanoid", "biped".
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>>If you're suddenly placed in front of a door, and told to enter, you may say "What door is this?" as in "is this the door to death, or riches", etc.
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>Then the proper question would be "which door is this"... but what if you wanted to ask what was the door of - is it wooden or iron or plastic... "kakva su ovo vrata?". "What kind of door is this" is not good enough, since I think you'd be PO'd both royally and republicly if you had tried all kinds of, say, fishing rods, and you ask "do you have any other kind", and they give you the same old just made of a different type of plastic. That's not a different kind, is it?

You'd ask, "Whats' this door made of?"

>Not that I mind much that you don't have this word - you never had it and don't feel that you're missing it, so no big deal. It's us who come from other languages who miss it :).