How do I get my "compulsory reservation" ?

Its a catch 22, but only on the surface. The TGV 9576 is nonstop from Karlsruhe to Strasbourg. For the last 5 minutes you are on the train between crossing the French border and Strasbourg station, who is going to go around and check seat reservations? It will still be a German crew running the train. If you wanted to stay on the train to Paris, you would definitely need a seat reservation.

Also, looking into May the purchase price of an advance purchase train specific ticket 2nd class ticket, a Sparpreis Europa Frankreich includes a seat reservation. 1st class always includes a seat reservation. The only one that does not include a seat reservation is a Flexpreis Ticket.

The reservations are mandatory when one takes the TGV, you cannot just board. When your ticket is checked, the controller is more interested in seeing your seat reservation than your ticket, that was certainly the feeling I got, at least twice.

Actually, looking closer maybe I do have one. It is really weird -- through the booking process it wouldn't allow us to reserve the seats. It kept failing at the last step and the red highlighted portion was the seat reservation section. It just wouldn't allow. Now I'm looking at the printout and the section for the TGV 9576 says :

"TGV 9576, 2 Sitzplatze, Wg. 5, Pl 87 88 1 Fenster, 1 Gang..." Google suggests this is window and aisle. I am guessing Wg is wagon (carriage)?

You do have reserved seats in Car #5.

Fred, when a TGV operates outside of France, it operates on that country's rules. No reservation is required in Germany. Same with Switzerland. Swiss just jump on the TGV Lyria in Zurich and jump off in Basel. That makes it a nonstop, and part of the half-hourly nonstop service between these 2 cities.

Italian EC trains require seat reservations, until they enter Switzerland.

Thanks for the information. I'm taking the TGV from Paris to Frankfurt, r/t, which I thought the reservation was still mandatory after the TGV crosses the border. You still stay seated in the same seat anyway from beginning to end .

"TGV 9576, 2 Sitzplatze, Wg. 5, Pl 87 88 1 Fenster, 1 Gang..."
= TGV 9576, 2 seats, coach (vehicle) 5, seats 87 and 88, 1 window seat, 1 aisle seat.

"compulsory reservation" is misrepresented. What is means is that when you buy a ticket on that train, it automatically includes reserved seat(s). It is physically impossible to buy tickets for a "compulsory reservation" train without the reservations. Sometimes you are given a choice of seats, sometimes (as in your case) it just allocates seats randomly.
In this case reserved seats are only compulsory for the last 2 Km from when the train crosses the Rhine until Strasbourg station (not while the train is on German rails), so not significant.

You only need to buy a reservation as an extra transaction if you are using a pass.

Thank you all for helping me figure this out.

Thanks, I received some more valuable lessons!