What's the proper track to learning PCB Design?
My first question is do PCB designers exist for separate domains ? If so, what are those domains?


A PCB Designer does exist for multiple separate domains.  For example, you can have a PCB designer that his main focus is High Speed Signal or another one that has more work experience in high power design.  At the end of the day, PCB designers work together as a team to get the best design possible.  Eventually, a PCB designer will become well rounded with tricky subjects like Mixed Split-planes, vias, and signal integrity.  


Second, if I want to pursue a Design career in this, what kind of study track exist. I mean is it a masters level course in Electronics? Or a masters level course in CAD/CAM ?


A typical Bachelor or Master in Electrical Engineering will get you the basics about PCB designing normally.  But for the most part, you will have to learn on your own to start off.  Upon landing an entry-level position with a PCB designer, you will work your way up and learn about those tools.  It all takes some time to become an expert in this domain but there is no real study track for designing PCBs.  Eagle is a good introductory tool to start off but you will want to become an expert with OrCad, Altium, or PADs in order to land a PCB designing position.