When did sputnik 2 return back to earth?

There were in fact several Sputnik satellites, but I imagine you're asking about the very first.

Sputnik-1 spent 3 months in orbit before re-entering and burning up. It was launched on October 4 1957, and was destroyed on January 4 1958. So it's location today would be... nowhere. It's believed to have been destroyed entirely. There is one piece left of sputnik, http://en.wikipedia.org/wiki/Sputnik_1 This metal arming key is the last remaining piece of the first Sputnik satellite. It prevented contact between the batteries and the transmitter prior to launch. Currently on display at the National Air and Space Museum.