[SOLVED] Anybody knows what cable I need for this MIDI port?

[FilmCraft]

(It's on my electric piano)

 

[Aeacus]

All MIDI ports are round:

What you have, actually don't have, is MIDI port on your hardware. Perhaps another model of electric piano has MIDI port but since yours doesn't, most likely, the outer casing mold is same for many models and which models doesn't have MIDI, their port hole remains closed. As yours is.