where is the plungeer vent clyonoide located? on 2008 Chevrolet Cobalt

code 455 and 496. I have changed the gas cap.

for p0455, you can try this:
Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.
Otherwise, replace the gas cap, and/or
Inspect the EVAP system for cuts/holes in tubes/hoses (you may hear a vacuum noise or smell fuel), repair if necessary