I want to write new adaptive plugin based on the student’s progress in learning the domain topics by using fuzzy logic. where I can start writing code?
You should first use Moodle a little bit. There is a nice Moodle course going on now, that uses Moodle and teaches you about Moodle.
After that, or right now, install Moodle and learn about the different plugin types.
Then choose the plugin type that you want to make. It might be an activity module, or quiz question type.
You can read about developing plugins for those types here:
https://docs.moodle.org/dev/Activity_modules
https://docs.moodle.org/dev/Question_types
All the developer docs are here: