Hey Vikrant, 

The syllabus for GATE Instrumentation Engineering will be released soon in the month of September or October.

For the time you can refer the previous year syllabus for preparation and be ready for the syllabus of 2020.

Main Subjects to be studied for preparation are :

• Engineering Mathematics
• Electrical Circuits
• Signals and Systems
• Control Systems
• Analog Electronics
• Digital Electronics
• Measurements
• Sensors and Industrial Instrumentation
• Communication and Optical Instrumentation

For more information regarding GATE Instrumentation Engineering syllabus, refer to this link :

https://engineering.careers360.com/articles/gate-syllabus-for-instrumentation-engineering/amp

Good Luck!