Whatever "communication agreement" is supposed to be, the term they used is some bad translation for, there isn't anything by that name on anything I know of.
What wires are in that cable?
If it's a single wire, then there's something called "one wire protocol" that certain displays use (there are some threads around here that show some of them). If your display is that kind, then you can connect it to that per the display's instructions.
If it's more than one wire, you'd have to find out what protocol it uses, to see if your display says it matches / supports that protocol, and then wire it up to the display per the display's instructions.
It might not even be for a display, but rather for programming it, in which case you'd need to know what kind of programmer, what protocol, where to get the programming software, etc.
None of this stuff is really standardized, so the best that can be done most of the time is to guess based on prior experience and whatever information you can scrape up about similar controllers from the same brand. (different brands may use totally different wiring, protocols, etc., and different sellers may use totally different bad translations of terminology).
So...if you are using a different brand / model controller than the bike came with, you may have to change out other parts on the bike to match the new controller, especially displays, sometimes PAS or torque sensors. Not every controller even supports a display or a PAS or torque sensor or throttle, etc., so when replacing or upgrading you have to find out what the original was, supports, etc., then find a new one that does the same things with the same wiring and protocols, or else replace all the incompatible stuff at the same time by using a kit that contains all those items plus the controller you want to use.