Access the frame of ROOTOpenGLView

I want to be able to access the ROOTOpenGLView in the QuartzWindow in my application. I am unsure of how I can get to it from TApplication or TCanvas.

Well, if you know Obj-C and Cocoa you should not have any problems accessing any view then.
Start, for example, from: … on/windows

having access to a window, you can access all views.

TCanvas knows nothing about NSViews - all it has is ‘winId’ - which is some integer (essentially index or key, known/understood only by TGCocoa internally).