my first ever job & piercings

I would show up with the retainer in but ask how they would feel about you wearing a small stud in the future. Same with the cartilage although most places don't have an issue with that. I guess it depends on where you're working but it's best to come dressed as they tell you unless they tell you otherwise how they feel about those rules

Ask them at the orientation before you do anything I got hired at 2 different places that said no visible piercings or tattoos...I went for orientation and ask them did I have to remove my nose ring or put a retainer in they told me as long as I wear a small stud and no hoops I can keep it in.. I also have a hand tattoo but I mostly wear gloves at work so they said my hand tattoo was fine also.. 

How long have you had it? A clear (glass) retainer would be the best option. If you've had it for a while, taking it out for a shift should be safe. I've had to do it for 3 years at a former job