For hardware with preinstalled (OEM) Windows 8.x and Windows 10, buyers don’t get a valid key printed on the device’s back or under the battery (for notebooks). The windows installer doesn’t even ask for a key anymore or the answer is skippable. If you still want to know your key to validate your fresh installation (on another pc) you can read it using the acpidump command under linux. For ubuntu install the package with:
sudo aptitude install acpidump
and read your serial with:
sudo acpidump -n MSDM