Can anyone tell me if you can do Aurangabad in one day including the Ellora and Ajanta caves. Or should I take two days?

And, if two days...any suggestions for additional sights etc in Aurangabad. thank you

You need two days, they lie in different directions from Aurangabad. There are some other sights in and around Aurangabad, although not in the same class, check a guidebook.

In addition to what thursdaysd has said, Ajanta is 100 kms from Aurangabad - doing that alone in a day from Aurangabad gets quite tiring. Keep in mind you'd deal with crowds there, especially if its a weekend or school holiday - it's harder in Ajanta due to the layout of the caves as well as the setting (halfway up the gorge of the waghora river). In Ellora, there are a few caves that almost no one visits or they'd be less crowded though still interesting. Other notable points of interest are Daulatabad fort and Bibi ka maqbara. Also, Ajanta and Ellora are closed on different days (Monday / Tuesday respectively), so factor that in as well.

Thank you

Two days are a must.
The 6th Mughal emperor Aurangzeb lies buried at Khuldabad (near Ellora Caves). It is an open grave, unlike other islamic tombs, a simple platform made of red stone with a "cavity" in the middle measuring a "few fingers" - as ordained by the emperor himself!
Before arriving pick up a book by Hansen Waldemar, 'The Peacock Throne'. You will love reading it.

Thank you