Some important development docs are found on the docs site: https://docs.luanti.org/
Notable pages:
- Releasing Luanti
- Engine translations
- Changelog
- Organisation
- Code style guidelines and Lua code style guidelines
- docker.md: Developing luantiserver with Docker
- android.md: Android tips & tricks
- os-compatibility.md: OS/library compatibility policy
- profiling.md: Profiling instructions
Oftentimes knowledge hasn't been written down (yet) and your best bet is to ask someone experienced and/or the core developers.
Feel free to join the #luanti-dev IRC and ask questions related to engine development.