iPad Pro 12.9 (2018)
Viewing data usage
You can see how much mobile data you've used when you've used the browser or sent and received email messages etc.
Press Settings.
Press Mobile Data.
The total data usage is displayed next to Current Period.
The data usage for each application is displayed below the name of the application.
Slide your finger upwards starting from the bottom of the screen to return to the home screen.