There is essentially no limit to how much physics you might learn...

. That being said electromagnetics is the foundation for optics, photonics, antennas, microwaves, fiber optic communication, radar systems, particle accelerators and lasers (along with an adjoining knowledge of semiconductor physics, solid state and quantum mechanics).
For control theory there are multivariable, adaptive, stochastic, optimal, and nonlinear coursework. You would be well served to have a knowledge of linear systems, digital signal processing, microcontrollers, etc. It can be very hands-on or purely sitting behind a desk using a CAD.
Control theory is kind of a subject unto itself. Very cross disciplinary with basic knowledge you could ply your trade on mechanical, fluid, aerospace, electrical, nuclear or chemical systems (called process control engineering). All involve classical physics knowledge of some type.
Control EEs are employed by many different industries. I know EE controls engineers working in semiconductor fabrication and power generation but the field is much, much broader. Probably most industrial processes that are above the most trivial design had a control engineer involved.
One other thing that is not quite as obvious is that many EEs perform control work as part of their routine job in say circuit design or even communication systems. so they are not "Control Engineer" by title but de facto.