Hey Manjunath! Joint Entrance Examination conducted by National Testing Agency covers almost all the topics from standard 11th and 12th course book. So there is no special preference given to any topic. If we talk about the tough questione asked is completely depends upon the candidates who prepared for the exam. Oscillation and waves, Gravitation, thermodynamics, rotation motion are some of the topics with tricky questions. 

Dear student here are some topics from physics from which difficult question may be asked

• Rotational Motion – Can occasionally daze you with a nice little whirl – and hence does justice to its name. Problems about angular momentum conservation are among the toughest in mechanics.
• Sound Waves – The most effective way to deliver this topic would be with the assistance of virtual aids.
• Wave Optics – Most people invest too much attention into Ray optics, and skip huge chunks from wave optics. Any topper would heavily advice against this – A cardinal rule of ‘Omit nothing’ is to be followed through and through.
• Fluids and Surface Tension – An occasional hiccup that can be avoided only by grasping concepts thoroughly.
• Modern Physics – Consists of theory questions with options cleverly shaped to deceive

All the best 

Hope this helps