I think you meant, "what should I call someone who comes after me as a night shift worker."
In that case, I don't think there is anything special you would call them. Coworker, of course. One thing you might call them is your, "relief," because they are there to relieve you of your duties for the day. That is not specific to night shift workers though. When you came back in the morning, you'd be their "relief".
I may have misunderstood your question though. Anyway, I hope this helped. Good luck!