I think here is the answer to this specific problem. I copied this from another Post.
For me it worked! Please check it ...
"As it turns out this is easy to do, if you realize that the watch is trying to respect your phone settings.
Here's what I did:
1. In the Apple Watch app on the iPhone, for the Mail settings, I said "Mirror my iPhone"
2. On the iPhone, In the Notifications settings for Mail, go to your Gmail account and click on Notification Sound
3. Under Vibration, pick one of the vibration settings other than None. Making this something other than None turns on haptic/tap on the watch, because the watch is trying to "mirror your phone"
4. Go back one screen from Vibration and pick "None" for Alert Tones. This turns off the sound on the watch too!
The same applies for other apps on the iPhone/Watch combo (calendar, iMessage). Changing the vibration and sound settings in the iPhone's notification settings affects the watch for those apps as well. I think most folks don't realize this, and it may explain why many people say they don't get notifications on the watch at all. They may have the notifications turned off on the phone, or alternately, have vibration and/or sound turned off for the notification on the phone."