I did the flash card thing in the academy for various penal, vehicle, health and safety (H&S), business and professions (B&P) and welfare and institutions (W&I) codes. They drill you on the most common ones, want you to give the elements, whether it is an infraction, misdemeanor, wobbler (a crime that can be charged as a misdemeanor or felony) or a felony.
Once you get to your agency, they give you their radio codes, which differ from region to region, county to county and in some cases, agency to agency. Most counties are pretty standardized. There is a 9 code, 10 code, 11 code.. those can be found on-line and as I said, they can vary from one area or jurisdiction to another. Most agencies use a combination of all 3. You would also get a shitload of city and county ordinances to review and be expected to be proficient with. You need to know how some differ from a similar state code and what elements need to be satisfied. Believe it or not, you also need to know what evidence needs to be collected for what crimes (which also differs when the suspect is a juvenile or an adult) and what specific forms need to be completed for each type of crime and each type of defendant (adult, juvenile, probationer, parolee, ward of the court, etc..).
For the most part, you are expected to know about 2/3rds of the radio codes and all of the various state, county and city laws that you would encounter on a regular basis. It just comes with time and repeated use. It is not nearly as important to KNOW a majority of the exact code numbers and subsections as it is very important to know 1) the elements of crimes (that there is even a law, then what the elements of the law) and 2) where to look to get the specific code section(s) for a ticket or booking sheet.
As for the vehicle, penal and W&I, H&S or B&P codes, unless it is a section I cite or use daily, I always verify the code section when I am writing a ticket or submitting a booking sheet or a report with a request to file charges. I have a cheat sheet, quick code and the code books (or trimmed down versions) handy at all times, so it takes me about 2 seconds to check and verify each code section. Often I find even better sections to use (which are more applicable or carry enhancements). It is much easier to check each time than to do a correction down the line. It also shows more professionalism, in my opinion.