A Waveform Monitor gives you all the information you need,but you need to look at it as well as the viewfinder---difficult unless you have two heads!
That said,with a little experience,you should be able to see the exposure level reasonably well,just looking at the picture on your viewfinder,assuming it looks at the video output.
Broadcast cameras
were fitted with automatic systems to do this,but they were usually too slow & were not used.
Instead,a Camera Control Unit operator watched the levels on a Waveform Monitor & adjusted as they went along.
A particular nightmare was when a football player ran through the line of shadow from the grandstand.
One moment--perfectly exposed,next---down in the blacks--adjust like mad,then he kicks the footy,& it goes to someone standing in bright sunlight---instant overexposure & white clipping.
Even HD Digital Broadcast cameras suffer from this problem----I suspect that they leave them on "auto".