How do you clean ventilation chamber in gas cook up downdraft

You can't modify gas appliances.

It is possible to remove the downdraft equipment from underneath your JennAir electric cooktop and still use the cooktop, but it depends on how the downdraft equipment is attached to the cooktop and whether there are any other issues that may arise from removing it.
Before attempting to remove the downdraft equipment, you should consult the user manual or contact JennAir customer service to ensure that it is safe to do so and to obtain any specific instructions for your particular model.
Some potential issues to consider when removing the downdraft equipment include:

1. Airflow: The downdraft equipment is designed to help draw smoke, steam, and odors down and out of the kitchen. Without it, you may experience reduced airflow and ventilation, which could result in lingering odors or smoke.
2. Heat distribution: The downdraft equipment may also help distribute heat evenly across the cooktop surface. Without it, you may experience hot spots or uneven cooking.
3. Stability: The downdraft equipment may provide additional support or stability to the cooktop. If it is removed, the cooktop may become less stable or secure.

If you decide to proceed with removing the downdraft equipment, it's important to follow all instructions carefully and to take appropriate safety precautions. You should also be prepared to address any issues that may arise as a result of the removal, such as by using an alternative ventilation system or adjusting your cooking techniques to compensate for any changes in heat distribution.
If you're unsure about whether or how to remove the downdraft equipment from your JennAir electric cooktop, it's best to consult with a professional technician or contact JennAir customer service for guidance.

what smell? electronics, burnt toast, dead rats? updraft, downdraft, in your lady's chamber?

We have a Viking VIPR101 30" downdraft ventilator. We've learned that the ON-OFF switch on the side of the ventilator can overheat and burn out when it is held down continuously (poor design). Best to push and quickly release it. First time we had the switch professionally replaced--it's modular and very simple to swap out. Next time we fixed it ourselves with switch part # PV300182 from allvikingparts.com. They had replacement guidance on-line. Hope this is useful.

yes via an exhaust vent to prevent carbon monoxide poisoning.

The downdraft is electric so there must be something malfunctioning with it. It is a high volume downdraft fan that is to be vented to the outside. Could it be that something has clogged the vent hole up, not allowing the fan to evacuate the smoke?

While I am not a big fan of Jenn-Air, their fans are usually high quality if they are installed correctly, with the proper vent lines.

You should just be able to set the cooktop in after you attach the downdraft, usually there are tabs on the downdraft that clamp on to the granite cutout. There is probably a closed-cell foam strip that runs under the lip of the cooktop, I would just make sure it seals to the granite properly (no gaps) and put a couple dabs of silicone in between the lip of the cooktop and the granite. Usually the cooktop is heavy enough that the silicone will keep it from moving around.

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The poupose of either is to eliminate any smoke created by the range or grille and move as much of the cooking odors to the outside. I wouldn't use both at the same time, but if the hood is vented to the outside, it would be just fine to use only the hood. Aregular cleaning will be necesssary. The downdraft has limits as to the distance it will efficiently exhaust air. Flex hose should not be used. And excessive bends or vent length, cuts into the efficiency.

No. If it is really important order the grates and downdraft cover as replacement parts. This will be expensive probably around $200 - $300.