Installed Windows 10 in a VirtualBox VM, is it possible to find the OEM product key?

I have an HP Z230 workstation which came with Windows 8.1 Pro downgraded to Windows 7 Pro preinstalled.

I have since replaced the harddrive and installed Ubuntu 16.04 on it.

I have also installed VirtualBox, and installed Windows 10 Pro in a VM.

From looking online I understand the product key is in the UEFI firmware?

The activation screen in Windows 10 says:

We can't activate Windows on this device because the previous version of Windows was not activated prior to upgrading to Windows 10. Go to the Store to buy genuine Windows. Error code: 0x803F7001

Questions:

• Am I able to use the Windows 8.1 product key from my bios to activate Windows 10 in my vm?
• If so, how can I retrieve the product key (using Ubuntu 16.04)?