Which is gramatically correct 'in the mall' or 'at the mall'?

Answer 1

Colloquially you can use either, but if you were to say 'in the mall' you would likely be referring to an object. There's a bookstore in the mall. If you said 'at the mall', you would presumably be referring to a person. Where is John? He's at the mall with his girlfriend. Of course, 'mall' can mean the physical building complex, in which case anything can be 'in' the mall, but 'at the mall would almost always refer to a person.