Easiest way to find info is to search the forum for “devterm gpio”.
I hope it’s possible to connect your eink display, but it won’t be trivial. From what I’ve read there aren’t many available GPIO pins on any of the Devterm models, as they are already used internally for other stuff. If you got really lucky and the default display and eink display required the same pins (though almost certainly in a different order) you may be able to build some sort of adaptor.