The computer will reset the light off if the condition that sets a fault code goes away, usually after a couple of "Good Trips" which occur when you drive the vehicle in the same conditions that the code set under. Evaporative emissions self tests usually occur right at start-up of a cold engine,with between 15% to 85% fuel tank levels. It may take a few days of driving with no problems found in the system self tests before the light will "Reset" itself.

As mentioned, you can disconnect the battery and you can clear all codes, but if any of the self tests or comprehensive component tests fail, the light will come back on.

Many chain type parts stores and auto repair shops have a code scanner and will pull any codes for you for free (in the hope that you will buy parts/repairs from them). It may be worth buying a cheap OBD-2 scanner if the light keeps coming on. With the actual fault code, it can lead you to a better diagnosis of what the problem is.

Good idea, I will try a new gas cap, but I think that the one on the Jeep now was an add-on the previous owner put on because it matches the other trim. I suppose some kind of trim package? Anyway, I'll see what I can find.
So about how much would the code scanner be?

I bought a creader v for $180. Only gives you the code number and small description. Only works on OBD-II. It has been worth its money many times over though.

Hey, thanks. I don't know right now what an OBD-II is. Ha ha, I can hear Big Jim laughing. I would have to google that one.
Meanwhile, I did check out your new Tracker build and I have one concern, which I posted on the site with the pictures.