In law school, you don’t generally specialize because you need to learn a wide spectrum of different areas to pass the bar exams. However, someone who likes to write might go into appellate advocacy, which is reviewing briefs and/or trial transcripts and preparing written appeals and could (depending on the firm you are with) include arguing the appeals before the court. I am a trial attorney but I also handle cases so I write motions and briefs. I have written some appeals and have found that the style of writing and what is required is different that the usual things that I do. At my firm, we have attorneys who specialize in appeals.
I took some journalism courses but not specifically for legal writing. I did find that the discipline of journalistic writing was helpful to me in my legal writing, much more so than the creative writing and play writing courses I took. However, I don’t think a journalism major is necessary for good legal writing, though a basic course or two couldn’t hurt.
You could also consider teaching writing at a college or law school or becoming an English or history teacher. Maybe teaching writing, as in AP classes, might appeal to you.