The most likely place for checking which wrist a device is on would be Health Services, however it seems the API doesn't expose any data on which wrist the user is wearing the device. I'd suggest asking your user this and saving it as an app setting.

You can, however, get info about physical buttons on a WearOS device using the Wear Input library, where getLocationZone() will tell you where on a device a given button is located.

Note that this will have to be done dynamically by your app whenever you need to do something with a button location - Unlike the Apple Watch, every WearOS device has different locations and even amounts of buttons and you can't guarantee that a user will use the same watch with your app every time.