Hello and welcome to the forum,
what data i need to collect for an application
This is far too large a subject for a forum topic.
It is also not the responsibility of one person to to deal with. Proper application testing includes having the proper data to test every function of every program and screen. You need to talk with your seniors or manager to learn which part of this effort you will work on.
Can anybody tell me about INSYNC tool
From which venfor? There are several "insync" tools available for different platforms. Our topics primarily deal with mainframe products and practices.