On the Rocker panel, if you have them
You don't need to climb under the car to see these jack pads if your car is equipt with them. They will be almost right behind the jacking hole in your rocker panels. If you don't feel or see a rubber pad right behind them, then your model doesn't have them. Not saying you couldn't construct a rubber pad on a board to put on your jackstand to serve the same purpose. There are rigid body molding or framing under the car at this area as well that would serve nicely as a support point.
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan