How to check the transmission fluid

Welcome back. That is one of the "filled for life" transmissions. ZF decided that average people shouldn't be able to do anything with it.
To check it there is a specific tool # 307-452 that does make it much easier but a stubby 8MM will work. If you want to make it easier you can use an 8MM 6 point wrench and a cut off section of an 8MM hex to imitate the OEM tool. It gets the tool closer to the plug and lets you hit the wrench easier. The plug will be very tight and the OEM is also loc-tited in.

The process is to get the vehicle in a level position high enough that you can get under it.
The engine will be running to do the check so be sure the car is very stable and level. Don't check the fluid with a hot engine, you want the fluid around 80 degrees.

Next you remove the trans cover tray (img 1).
Now get in the car, step on the brake and put the transmission into reverse for three seconds, then shift to drive for three seconds. Finally back to park. Leave the engine running at idle.
Now go under the car and locate the check/fill port on the right rear of the transmission just above the pan flange. Remove the plug. If the fluid level is correct some fluid should come out. As soon as the plug is out. If no fluid comes out add fluid until it does come out. Reinstall the plug. Jaguar calls for a torque spec on the plug but I just tighten it very snug.

If you change the fluid you use the drain plug in the plastic pan, then refill through that same check/fill port above. Be sure to use the correct fluid.

You're welcome. Please return anytime with your automotive questions.

The specification for the ZF 6H26 transmission you have is for Shell M1375.4
However, that same transmission has been used in other vehicles so you can get the fluid for a better price than the Jaguar dealer wants. Fords Mercon SP Fluid Part No. XT-6QSP
Is the same stuff and much cheaper to get. There are a few others but in the case of the ZF transmission I try to use OEM fluids.