There are differences in meaning, but all of these are correct in a suitable context. I work tomorrow. I am working tomorrow. I am going to work tomorrow. I am going to be working tomorrow. I will work tomorrow. More information: https://www.ef.com/wwen/english-resources/english-grammar/future/

Both!

"I work tomorrow" is perfectly correct and also very common. Chris gave a good answer.

both of them are correct

Maybe it's a difference with British English but I wouldn't say "I work tomorrow" You could say: I have work tomorrow I have to work tomorrow I am working tomorrow I will be working tomorrow I am going to work tomorrow (implies more travelling to your workplace)