I would like to know which are the main article categories a journalist is expected to know how to write.
Some classic and actual article types are similar. Others were born recently, such as smartphone or video game reviews.
If this is a very broad question, don't hesitate to redirect me to books or Wikipedia articles.
I'm not sure if my list is comprehensive, but:
and minor forms like headlines or summaries(blurbs) for front page or RSS, live reporting (minute-by-minute newsfeeds), taglines and so on.
These are just forms of publication and they branch into hundreds sub-genres by subject. Smartphone or Video Game reviews are just form of Reviews, and while the subject is different, the structure is the same as reviews of cars or restaurants from a hundred years ago. Similarly, an essay on Higgs' Boson will probably be of similar structure as one on AC Voltage from times of Tesla (popular science) and one on biography of Diego Maradona will be similar to biography of Winston Churchill (biographical essay). So don't get blinded by the variety of subjects - the number of actual core forms of journalism is much smaller.
Also, these are for actual publishing, but you will be required to write letters to interviewees, request publications, write reports for your superiors, prepare polls questions and handle many more genres that never show up in print, but are necessary to perform the job.
(note there are also other forms of journalism but they are usually handled by respective specialists - photojournalism, live TV news reporting, copywriting etc, but these are rarely handled by journalists.)
I would say the classic story you should be able to write is the news story. Reporting accurately with facts and attribution about an event that is newsworthy (proximity, prominence, impact, human interest, currency, conflict, unexpected) This type of reporting on the most basic level is just lede --> quote --> transition --> quote --> transition ... walkoff quote. And the facts of the story are added in order of importance and urgency (inverted pyramid).
That's the most important.
But you also want to be able to write opinion which is less rigid but still follows AP style.
As for specific topics my suggestion would be to go onto a newspaper's website and look for trending topics. In the section of the paper you are interested in looking for.
Basically, there are different styles of writing for some of the sections in the paper (news is different from opinion etc). Then, when an editor is assigning a story they choose the section based on what is appropriate. I would learn how to write for the sections you want to (reviews, opinion, news, profiles) and then you can write about most of the topics you wish to. I hope this helps!
expected to know how to write.Expected by whom?