You've ever been to a junkyard? If you pick up a broken amplifier, it's not going to have a user manual taped to it. You're going to have to figure things out. This is essentially code junkyard. 13 years old and rusting.

You will need to find a development kit somewhere.

The documentation on this random website seems accurate

https://docs.huihoo.com/symbian/nokia-symbian3-developers-li...

OP Here. Found that there's a previous thread, with more info SDK tools: https://news.ycombinator.com/item?id=31492447

I'd try to build a textshell image, maybe the emulator or the beagleboard https://github.com/SymbianSource/oss.FCL.sf.adapt.beagleboar...

Oh look qemu too https://github.com/SymbianSource/oss.FCL.sf.adapt.Qemu

https://github.com/SymbianSource/oss.FCL.sf.adapt.Qemu/blob/...