When CS majors or programmers estimate how fast/efficient code is they generally are intuitively applying big 'O' notation or some similar concept. This can be gained from an intro level algorithms class. Or you could look up and read about the topic.
The classical coding interview questions mostly stem from an intro algorithms and data structures class. Or you could get a book on interview prep and work through a couple a day.
Finally, the coding style issue usually is ancillary knowledge and not found (or at least not done well) in typical CS curricular. I would suggest the book "Clean Code" by Robert Martin. It goes through code smells, commenting, general style, and is well written.
So overall, you could look at Algorithms and Data Structures MOOC's. Also read a book on CS interview prep and writing maintainable code. Hope this helps a little. Good Luck!