Those are good question I'm afraid I can't give a definite answer for.
I don't have any smartphone/tablet.
On my desktop computer, I do have some widget on the desktop that allows me to keep an eye on the performances of my nvidia graphic card, giving me the amount of VRAM used/available, usage percentage, etc...
I bet there are some apps available for your device that would provie the same service hopefully, but I have no link to give you.
Maybe other mobile-users will have an answer for you.
For now all I could advise you would be to try to find such an app in the appstore of your device and/or google about this specific device in case you would find the specs on a blog or a review website.