To my knowledge there aren't any watches on the market yet that measure glucose themselves (though I know it's being worked on).
So your options are a separate CGM or Libre device, with a Bluetooth link to a fitness band or smart watch (usually going via a smartphone too).
Ive just posted about this on another thread. I have an Apple Watch which I’m very impressed with but have read that Apple are at least 3 years away from getting a reliable watch for diabetes. So if a big company like Apple can’t manage it yet I wouldn’t trust any others just yet