Is it possible to know the last time my iPhone was online? My iPhone was stolen about two months ago, and the company wants to know the date which I lost it.

Is it possible to recover information to the last time it was turned on?
Go to iCloud - Find My iPhone, and select your device. You can also see where it is right now, and you can lock and erase it.

What's required though is that you have to had iCloud set up before it got stolen.