I have a Kenmore gas dryer. I'm not sure how to disconnect the gas supply to the dryer. Any help?

I'm guessing you wouldn't be posting if you had found a valve on the gas line near the dryer. If that is true, where is the next valve upstream? That is the valve that you need to turn off.

When in doubt, turn it off at the gas meter. That, of course, will shut off gas to the whole building (or unit in the case of individually-metered multiple dwelling units).

Whenever you turn off the gas at the gas meter, you will have to re-light pilots on any appliances that do not have spark or hot surface igniters.

If you are not comfortable with these terms and operations, contact a licensed plumber gas fitter or plumber.

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Links to the State of Wisconsin Plumbing Code:
[docs.legis.wisconsin.gov]
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I am not a plumber.
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there has to be a union behind the dryer somewhere.

CAUTION... you are tampering with natural gas. Be sure you know what you are doing. Gas will blow your _ss up. I recently saw a home that had just closed escrow. The previous owner had the flex connector connected to a nipple, not the adaptor that it is designed for. I can't believe it was connected that way before they moved and that it must have been screwed together by someone that was clueless. Just make sure you discuss what you are doing with someone that is knowledgable. Good luck..