To be honest, if you are a developer you should know. You need to check the code... where is the license check, where are some server requests for validating license data and so on. There is no "look here" solution. That is different in every code or software. Every developer implements such checks or validations different. Sometimes they try to hide it. Sometimes they also obfuscate some code. But as a developer it should be easy to find. Just look at the code. A good starting point is always the code, which is executed, if a license is incorrect. So just enter incorrect data and then search the code, which is responsible for that. From there it should be easy to find the license checks.