How to use “ 难道 ” in Chinese sentences?
Grammatically, "难道" is an indication of 反问句(a rhetorical negative question). The exact correspondence in English may differ depending on the context, but I will give some examples here:


  (难道)你不知道吗？ 
  > Don't you know it? (I thought that you knew it.) 
  你(难道)不知道……吗？ 
  > Don't you know that ...... 
  (难道)你不明白吗？ 
  > Don't you understand? 
  这难道不是真理吗？ 
  > Ain't that the truth? 
  (难道)你今天不用上班吗？ 
  > Don't you have to work today? 
  你不来吗？ 
  > Aren't you coming?



Personally, I believe it's sometimes better to put 难道 in the beginning, though most of the time, the order doesn't matter in spoken language.


Questioning with a negating particle 不(not) is a negative question itself. So basically they are the same in meaning.
The possible difference is: in the second question with 难道, the speaker believes more firmly that the listener should have known (the object), to the extent that he is/would be very surprised if the listener doesn't know anything. This may also be implied in the first sentence without 难道, again, depending on the context.