Resetting PRAM through Terminal
According to an Apple Support page called "Prepare your institution for iOS 10 and macOS Sierra":


  ...you must use the nvram command to properly set boot-args NVRAM variable. Starting with macOS Sierra, you must be booted to the recovery partition to run this command.


But now you can clear the NVRAM with

sudo nvram -c


Then restart for the reset to take effect.

I also have a PC keyboard that doesn't seem able to reset the NVRAM on startup, but I think the real problem is that it's wireless. But this command is easier and more reliable anyway.