No current or newly announced Apple Watch model offers glucose monitoring as a built-in feature.
Various third-party apps for iPhone - some of which include an app for Apple Watch - offer features that are designed to help with the recording and analysis of glucose levels, some when used in conjunction with specific third-party accessories.
One Drop includes an app for Apple Watch and can sync data directly from a Bluetooth-enabled blood glucose meter (available separately as a third-party accessory):
Dexcom G5TM Mobile Continuous Glucose Monitoring (CGM) System:
Dexcom G4® PLATINUM System with Share
Keep in mind Apple's Important safety information, which includes:
Not a medical device Apple Watch, the heart rate sensor, and the included Apple Watch apps are not medical devices and are intended for fitness purposes only. They are not designed or intended for use in the diagnosis of disease or other conditions, or in the cure, mitigation, treatment, or prevention of disease.
Important safety information