NSFW Acc: 
May I ask for some language help again, dear twitter people? 
When I say to my primary school English learners: "Today is Monday." and I'd like to ask for tomorrow's name of the day (Tuesday) - what do I ask?
a: "What day is tomorrow?" or
b: "What day will be tomorrow?" 
pic.twitter.com/v9KxpPrl5S
Although "tomorrow" is relative, the exact day it represents is fixed in the moment when you use the word. Tomorrow IS tomorrow^^ So saying "what day is tomorrow" is completely fine IMHO
