This app was mentioned in 3 comments, with an average of 1.67 upvotes
have you tried an app like this; Netlive https://play.google.com/store/apps/details?id=com.richardlucasapps.netlive&hl=en
>NetLive allows you to monitor your internet data transfer rate while displaying which app is currently using the most data
or
OS monitor https://play.google.com/store/apps/details?id=com.eolwral.osmonitor&hl=en
Ah. That's xposed + gravitybox.
I think there's another app that can do it too though: https://play.google.com/store/apps/details?id=com.richardlucasapps.netlive&hl=en
It's called NetLive. I found it looking for something else, but it looks pretty handy itself so I kept it.