I'm pretty sure this refers to the fuel vapor canister (part # 314203M500 for a 2015 K900). This is part of the evaporative emission control (EVAP) system and prevents the evaporating fumes from reaching the atmosphere while also maintaining proper fuel tank pressures.
In most Kias, (I don't know for sure, but I don't think the K900 is any different) it's accessed by removing the rear wheel on the side the fuel filler is located, then removing the wheel well liner. The canister itself is attached with a few bolts and a hose clamp.
The owner's manual states that the fuel filter and fuel tank air filter are considered maintenance free but recommends periodic inspection. The canister isn't cheap (about $200 just for the part) so unless you are getting trouble codes for the EVAP system or experiencing issues when you're getting gas like the automatic pump cutoff triggering well before the tank is full, or gas overflowing the tank I'd just leave it alone.
Best way to prevent problems with the vapor canister is to not "top off" the tank when you fill up. By that I mean once the automatic cutoff triggers, don't try to add a bit more gas, repeatedly causing the cutoff to trigger. Overfilling the tank can force fuel into the vapor canister. Liquid fuel can deteriorate the charcoal in the canister, turning it into small granules that can in turn travel through the rest of the system and stick in valves and solenoids, which gets expensive fast.