I will show you where the tea is. should be the preferred response, because it is grammatically correct and most native-like expression.
I will show you where tea is. is grammatically acceptable, but awkward, because it's rare to use the null article in thus instance.
I will show where tea is. is grammatically incorrect without an indirect object, and painfully awkward for a native to read, but it should be accepted as an answer even if it is unacceptable as English, because it resembles the literal translation.
Agreed regarding correctness, but incorrect English is not a translation and should not be accepted. The target language is not English here, but people who have taken the trouble to learn enough English to be able to follow this course will not thank us for including incorrect forms.
I agree with Lilalino. As far as I know "show" needs an indirect object in English. Who something is shown to cannot be assumed as in Russian. Therefore I think: "I will show you where the tea is" or "I will show him where the tea is" should definitely be accepted, too. And it should also be the preferred translation.