You have to climb the roof of the post office using the pipe on the wall of that building.

Thank you! But are you talking about the second building or third building? In the third building, there's stairs to get down and enter the building but I'm not finding any way to exit the building.

Can someone please tell me how to beat the goons and how to meet the spy who is hiding?

Good news, Sunnybhai, Hope we'll find the update very soon.