In my first programming job, I was given The C Programming Language and told to study it. So when I got my second programming job, I figured out what language I'd be coding in and started studying up.
This was a mistake. Supposing you want to study for a job before you start the job, language study is almost always the wrong place to put your hours:
Meanwhile, there is a likely source of confusion you can often address in advance: tooling. Ask about what the team uses for:
Sometimes these will be proprietary, and sometimes they will not exist. But often they will (exist and) be things you can read about and even practice with. I have always found this sort of thing much harder to pick up than a new language.
If you have only ever worked on small- to medium-sized projects and are about to join a company, consider reading Software Engineering at Google. Whether or not you're going to work at huge scale, and whether or not you like all the recommendations in the book, it's a wonderful menu of the problems that arise from any kind of real scale. Any chapter of that book would have been more valuable to me than all the C++ prep I did back in the day.
P.S.: This post is about what to do if you want to study for a job before you start it. I'm ignoring the question of whether such study is good, bad, appropriate, or whatever else.
P.P.S.: Follow-up here.