To see notifications such as text messages on your infotainment screen, you must enable notifications for Google Assistant.
You will be asked to enable notifications when you set up your infotainment screen with an Android device. If you are having trouble receiving notifications on your infotainment screen after initial set up, try the following steps:
1. On your car’s infotainment screen, navigate to Settings
2. Tap Apps and notifications 
3. Turn on Google Assistant