Dr. Danada helps prepare Daria for her interview for the Wizard Scholarship. It is also possible that he has has helped Jodie for the same interview. He has a Ph.D. (as stated on his office door), but what it is for is unknown.
Daria is initially reluctant about using him, considering it cheating, but eventually goes along. He bombards her with buzzwords about promoting herself - "you need to project 'winner' the moment you walk in the door" - before noticing she seems ambivalent about going for the scholarship interview at all. When she raises an ethical question about the prize, Danada stares for a second and then moves onto what she should wear. Later, Daria kicks herself for going to him after all her previous claims of integrity.
As "da nada" is Spanish for "it was nothing", his name is basically "Doctor of Nothing".