It means that Monika us asking Phibi Why does she need the atlas? does she need it because she has to submit a report? ( an assignment?) Monika is assuming that Phibi needs to refer the atlas to work on her report. Hope this helps.:)

'due' is for a scheduled thing that is coming up, eg: His train is due in at 7:50, or Her baby is due on the 29th. :)