Originally Posted by Goldorak

You can never be sure of your arrival terminal at CDG as it's driven by Schengen or non-Schengen arrival. So to make it short, from IAD, you can arrive at 2C, 2E or 2F. As Ireland is not part of the Schengen area, you won't have to clear immigration in CDG. No luggage to pick-up at CDG. They will be delivered to you in DUB, where you'll clear both immigration & customs.
DUB flights departs from 2E, so depending at which terminal you'll arrive, either you stay in the same, or you have to transfer from 2C/2F to 2E but staying airside. This means that you won't be able to use the arrival lounge at 2C because it's landside. But I'm sure you can try the regular nice 2E lounge (also equipped with showers). Even if you fly Y to DUB, I think you can access it showing your J boarding pass from IAD.