Where are the 2 catalytic converters located on a 2004 Chevy aveo

Cat converters are part of the exhaust system which are used for emission purposes. Not all vehicles have 2 some have more or less. Where your exhaust connects to the engine the first round fat part of the pipe that is much larger then the actual pipe is the first cat converter the second will look similar to the first one but usually slightly smaller. If your having a concern it’s usually the one closest to the engine. Side note, if you have a engine light on that says you have a cat system performance failure and it runs fine usually this will not cause any concerns other then the engine light. I say this because cats are not cheap, so if it’s running good and you don’t mind the light then drive it.