Should be: "What day is IT today?"
The sentence structure in English is not really correct. One could say "Which/What day is it today?".
What day is it?
I agree I said 'what day is it?' and its marked wrong
"What day is it today" or "Which day is it today" are both wrong.
In this case the Indonesian phrase "yang (mana)" should have been used if they want the given translation