I've been struggling to answer this question since the first chapter, but now I need to address it for the upcoming chapter.

If you're familiar with Final Filly Fantasy (if not... shame on you), then you're probably aware that Tempest Shadow is suffering from depression. Despite losing it years ago, the lose of her horn still shackles her. One of the things I'm hoping to touch upon is some dreams that she had as a filly that have been severed from this unique handicap, but I'm coming up short of what those dreams are as the only ones that come to mind are Magician and Buckball goalie (not enough examples to my taste).

Whatever the career is, it would have to involve the use of a horn, one that can't be resolved with lightning or firework spells like the ones she displayed in the movie. I would be grateful if you could give some examples.

But to keep this topic more open, feel free to throw out any careers that can only be performed if you were a unicorn or some magic using creature.

7703617 She wanted to be a professional basketball player, but all the balls she tries to levitate just explode. She will never be a basketball player. She will never be able to even levitate a ball.

7703617
Alchemy often involves magic. That could be one

7703617
It's not necessary that the job has to be one that nopony can do without magic. It just needs to be one that Tempest herself can't do without magic.

For example. she could have aspired to become a clock maker. Yes, there may be rare instances that some non-unicorn ponies are still skillful enough to manipulate all those tiny pieces of the clocks without magic. But not Tempest. She might just be inherently too clumsy with her hooves to do anything clock-related without her magic. You can even make it a general trait of unicorn race-wise, not as skillful with controlling their hooves compared to earth ponies for example because their brains are born relying on magic for precision (would explain why a lot of musicians are earth ponies).

Or, as 7703698 suggested, alchemist, or electrician, could be a good one. Tempest just couldn't do it because her constantly sparking horn would set every explosive stuff on fire outside of her control. Same issue with being an electrician.