1. Login to the g+ mobile app
2. Tap on the More option on the bottom right of the navigation menu
3. Scroll down and tap on Notification Preferences
4. Once in Notification Preferences, you can turn on or off the notifications you would like to receive.
* If you chose Decline when you first opened the g+ app when asked if you would like to receive notifications and you want to enable them again you will need to tap on Device Notification Settings in the Notification Preferences section and allow notifications for the g+ app.