Look for it in its network settings. It might be labeled as a physical address and, if your device supports both wired and wifi connections, it will have two. They are always in the form of 12 letters (A-F) or numbers, usually in pairs, like 12:34:56:78:9a:bc or 35-9a-2c-4b-61-d0. If you can't find it, we can likely help. We just need to know what kind of device you have.