Which one is correct?
1. What is the due date for uploading the documents?

2. When is the due date for uploading the documents?

3. When is it due?

Thank you in advance.

Question

Which one is correct?
1. What is the due date for uploading the documents?

2. When is the due date for uploading the documents?

3. When is it due?

Thank you in advance.

Answer

All of these are possible. I mean to say that a native speaker would understand your meaning for all three. However, the third choice "When is it due?" would be the most common.

Also, keep in mind that "the documents" are plural so you may want to say, "When are they due?"