I am using a HolyBro Kakute F4 V2 flight controller loaded with ArduPilot firmware. I am using Mission Planner currently. I wish to know how can I program the board so that I have some additional features such as fetching gps coordinates during flight etc.
The ArduPilot code is available on GitHub. Here you can also find links to the support forum and community, where you can get help with specific issues.
It's mostly written in C++, which isn't the easiest language to learn but it's very well established so there are loads of free resources. You can find plenty of tutorials, reference guides and free development environments and compilers.