Two great suggestions here to go on!
Bjarney's suggestion about the Public Library [which is where I did many Years of free Studying in Electrical Tech - with many odd looks from people in the Library, due to a Long Haired Joker with the day's dirt build-up on the clothes being in the Library's Reference area!], is great for discovering what books to buy when money becomes available.
Bill's suggestion is about the best way to cover the Code sections.
Some other suggestions would be to "Pop Quiz" or "Poll" questions from your workmates and / or boss[es] and Foreperson[s], then get their input or interpretations of the Code for reference and apply it against what the "Good Book" says.
Another one is to reference some of the commonly mentioned Codes [like color codes, receptacle orientation, ampacities, outlet height, box fill, and so on], and see just what is really in the book. You will be suprised what you find [or do not find] just concerning the ones I listed above!
Searching the NEC for these items will help you get a feel for the structure of the book.
From there, move into your Local Codes, which will normally be the ones you will work from.
In California, we follow CEC [AKA Title 24, part 6] in respect to Lighting.
Also, most installs will have ADA requirements, so that's another Code to reference.
Lastly, just post questions / examples to this forum. The members here are happy to assist. If you make your references "Life-Like", there will be more replies!
Try using "The Wigget Factory", or something to do with Wiggets as your example installation customer