CDG is the arrival airport in the Schengen zone, this is where you will go through immigration and passport controls.
Find out which terminal and arrival hall your flight is in.
Coming from Chicago with Air France this should be terminal 2E
From CDG to ATH Aegean flights depart from Terminal 2B.
Terminals are connected, within the public area, by walkways.
Between terminal 2E and 2B there is about a 25 minute walk
There is also a free shuttle (CDGVAL)
Here is a link to help you to get around CDG:
https://easycdg.com/airport-guide/travel-between-terminals-move-around-paris-cdg-airport/
3H10 is enough to make that connection.
Of course your flight from Chicago should not be delayed for more than 60 minutes.
To board the Aegean flight you will need to pass the usual security checks.
Since you are coming from Paris you will arrive in the Schengen area of Athens airport, so you will no longer have immigration or passport controls.