When you get to CDG, you'll need to clear immigration, get your bag, then go through customs. You can then take the CDGVal to Terminal 2, if you're not already there. Head to the station area, which is quite well signposted, and situated between T2C, T2D and T2E. You can spot it in the middle of the map on the airport website. Once in the station area, find the ticket office, find the badly sign-posted TGVAir desk (don't just the long main ticket queues!). Show them your ticket reference, they'll find your ticket which they should've already printed, stamp it, and hand it over.
At this point, look at the time. You need to be at the right point on the platform 5 minutes before scheduled departure, and I'd suggest at least 10, ideally 15 minutes before to avoid stress/worry. The platform should be announced 30 minutes or so in advance. That gives you your waiting time, which could be fairly short, especially if there were delays!
In the station area of the airport, there are a few cafes. I seem to recall there are some with power sockets, can't remember about wifi. I picked the one nearest the ticket office last time I was there, and it was fine to kill the time until the train. There area also some seats in the central area which are at a bench-thingy with power sockets, most of which worked. If you have under an hour, just pick one of those
If you have a long time, it's a 5-10 minute walk to much of T2, so you can always go for landside cafes there