Can you say: איזה מסעדה את זה?
No. "מסעדה" is a feminine word and therefore you need to use "זאת" or "זו", and also the word "את" should not be used here.
Et before zeh is only for direct objects. With the verb 'to be' we dont consider the predicate a DO.
Why EIZE MA'IL ZE was accepted as the right choice for "What is this coat?" but when I tried "What is this restaurant?" for EIZO MIS'ADA ZOT, it was rejected. If this answer is wrong, the previous one should also be wrong.
Can I use איזה for male and female nouns?
Zdeka is right, except that in spoken/colloquial Hebrew איזה is used more commonly (I think) than איזו also for feminine.
only for male things, for female things it is איזו.
Why not "what kind of" instead of "which"?
That would be איזה סוג של.