Hi

As per I know and my search reveals, for live doubt clearing, aspirants used to call (video) their teachers via different social networking sites. Try to consult your teacher regardind such doubt solving. If there exist any live doubt clearing app, I think it might not be for FREE. 

For doubt clearing (just about live) you can put your queries on this only app Careers360.com , as on this platform you can get the advice from people already in the field for which you are competing.

Hope this info be helpful.

All the best.