The upper left hand corner of the frame can be achieved with frame.getLocation().x and frame.getLocation().y... but you want to account for the insets? Can't you just use frame.getInsets()? I guess I don't understand your problem.

The following sketch works for me:

1. void setup() {
2.   size(400, 400);
3.  
4.   strokeWeight(10);
5.   smooth();
6. }
7. 
   
8. void draw() {
9.   PVector screenLoc = new PVector(frame.getLocation().x + frame.getInsets().left, frame.getLocation().y + frame.getInsets().top;
10.   println(screenLoc);
11.  
12.   //Center the sketch window in the screen to see the point
13.  
14.   background(255);
15.   point(screenWidth / 2 - screenLoc.x, screenHeight / 2 - screenLoc.y);
16. }