Reservation (TGVs) and WiFi (TGVs and ICEs)

"Does this imply that there is no reservation compulsion once the train crosses the border into Germany" - Yes
Whether the train is actually a TGV or an ICE (both models are used on Paris - Germany routes), it is subject to SNCF ticketing rules (reservation compulsary) up to the border and DB rules thereafter.

Your second question is a totally different train. I guess this train is starting from somewhere in Switzerland (Zürich?, Interlaken?), then going via Basel, lots of other places and ending in Kiel, on the Baltic Sea. These trains change crews at Basel SBB station, and change over from SBB to DB responsibilty. My guess is that they have the infrastructure for WiFi all along the DB lines, but not along the SBB lines in Switzerland. SBB does not yet offer WiFi.
"Bordrestaurant Wifi" to me implies WiFi is only available in the Bordrestaurant (=restaurant car).

Chris:

Thanks for the response. I can save the phone call and confusion then; we will travel lower deck for two hours and then scoot up and see if we can find a place on the upper deck (hopefully, it won't be a mad scramble - these trains should not be too full, right?)

And yes, the second train is Basel to Kiel. Is the WiFi on these trains for free or for pay?

TGV's are usually fairly full. The ticket pricing system is desgined to maximise income, and this keeps the trains 90%+ full.
At Saarbücken, if you move to a seat reserved by somebody getting on a Saarbrücken, or a later stop, you will have to move again.
Sorry, I don't know if you have to pay for WiFi on DB trains.

Looks like it costs. This is from the DB website:

Therefore click in the section “How to become a HotSpot customer”.
You don’t need a contract with Deutsche Telekom. All you need is your
credit card (Mastercard, Visa, American Express). Please refer to the
Internet HotSpot Portal (www.HotSpot.de) for cost information.
 After entering your name and your password click the and
you are online.
The HotSpot Pass you buy in Germany is not roaming-capable, so you
can’t use it when you’re in other countries!

Since the TGV operates nonstop between Paris and Saarbrucken, when the conductor checks your ticket, ask him if you can move to the upper deck. You can go up and see what the seating situation is as soon as you depart Paris Est. I do not recall if there is any rock solid rule the you HAVE to sit in your assigned seat. Apparently Italian Freccia trains do that now.

Our trains were all relatively full that day, and we did not consider moving to a different seat on the TGV. Our bags were solidly occupying their space. :-)

Kids and I did spend quite a lot of time in the pantry car (which was on the second level - come to think of it, I did not even see what was there in the lower level of that car) and enjoyed the seating, the view and the conversation with the friendly rep who was originally from Mauritius but now from France.

We did not even try to use the WiFi - were too busy seeing the sights and taking photos. I believe we hit 320 kmph at the max.

Porcupyn

Thanks for reporting back. Your experience sounds like what I would have expected.