is this sentence grammatically correct (狐狸精在那里?)?

Yes.

Why? you looking for 狐狸精? I assume you know what that is, right?

Oh...if that's what you want to ask (where the sluts are), then you're using the wrong term. 狐狸精 is a woman who steals someone else's husband.

yes 100% correct. don't listen to others this is a very usefull phrase that can be used a lot in china for business and pleasure.

It is grammatically correct.

Yes!
But who are you asking 狐狸精在那里 to?
lol

The grammar is correct but I think you shouldn't being using that phrase if you are in China.

What is
狐狸精在那里!