هُنَاك
What grammatical case is used with it ?

See a translation

@olusialeks
I'm not sure what you mean. Do you mean sentences like هناك رجل which means "there is a man"?

If yes, then هناك does not affect the case of neighbouring nouns. BUT USUALLY, the nominative case comes after it:

هناكَ رَجُلٌ (there is a man)

If you use words like كان or إن that alter the cases, you treat رجل as the subject, so you say:

كانَ هناكَ رجلٌ (there was a man)

or

إنَّ هناكَ رجلًا (indeed, there is a man)

So in summary, هناك doesn't affect cases at all. But usually, in simple sentence, you use the nominative case after it.

I hope this was helpful