If I want to ask what days that a restaurant opens to public, which the following sentence is correct?
What days are the restaurant open?
What days is the restaurant open?
The answer is Monday, Tuesday, Wednesday and Thursday.
If I want to ask what days that a restaurant opens to public, which the following sentence is correct?
What days are the restaurant open?
What days is the restaurant open?
The answer is Monday, Tuesday, Wednesday and Thursday.
I would choose two. The subject is the restaurant, not days.
If you simplify, you'll will see this better.
When is the the restaurant open?
If you answer the question, it also becomes clearer.
The restaurant is open Mondays through Thursdays.
In my opinion the two sentences are grammatically wrong , it's better to rephrase the question with " Do you know which days the restaurant opens? but Number 1 is wrong because he is talking about the restaurant which is only one restaurant and a singular quantity so it takes is.