Firstly, there are many types of paid writing work across a diverse range of disciplines from writing scripts, books, journals and newspaper articles, to writing marketing content. There are also as many subjects available to write about as there are diverse human experiences, after all writing is quite literally the translation of human experience into an artful literary presentation.
Writing is not like regular jobs, even if you do find yourself in a standard office environment the chances are it is unlike any other office based career. The experience of a writer is more in-line with that of a musician or artist. It takes more than just training, most importantly it requires talent and an extraordinary level of dedication. Becoming a professional writer takes time, will lead to several knock backs and you must be prepared that in the end it could never actually happen.