How to detect if VT-X has been turned on in the BIOS?

VT-X information is stored in model-specific registers (MSR) 0x34 which can be accessed via msr-tools. Install it by running sudo apt-get install msr-tools then run the following commands

sudo modprobe msr
sudo rdmsr 0x3A

If the return value is 3, 5 or 7 then VT-X is enabled

See Reliably detecting if Intel VT is disabled in the BIOS