The Evap core is part of the AC system. It is the small "cold radiator" component up under the dashboard. Air comes through it first and is cooled then into the car. Cold and condensation make it attract more dirt. It looks very similar to the heater core- also under the dash. Both are very close to each other and packed into the ventilation system. They can both be accessed by removing 3-4 dash/ventilation panels. Be prepared to lay upside-down for awhile.
However, you cannot completely remove them without opening the heating/coolant system and the AC system. You risk creating future "leaks" in either system if not careful, plus they will need to be charged/refilled once reconnected. This is why I decided to loosen the heater and evap cores to pull them out a little as much as possible (and it ain't much) then reach up behind the Evap core to brush it off.
The heater core right is in front of the evap core, so once you locate the heater core- the Evap core is in the next panel behind it almost up against the inside firewall. Good Luck!!