The exam pattern for JEE Advanced is never disclosed by the IITs. However you can always get an idea from the previous year question papers to prepare. Check the exam pattern gauged from past years here. https://engineering.careers360.com/articles/jee-advanced-exam-pattern

This year things may be slightly different as the exam is going online for the first time so nobody knows anything as of yet. We will be updating all information as and when it is announced.