when i update my ipod touch to ios 9.2.1, my wifi stoped working

Have you tried Restarting the iPod at least?

If not:

iOS: Wi-Fi or Bluetooth settings grayed out or dim

One user reported that placing the iPod in the freezer fixed the problem.

Also heating sometimes works. See:

Why can't I select my wifi settings?

A trick that works frequently with iPhones:

Settings > AirPlane Mode ON, Do Not Disturb ON

Power down and wait 5-10 minutes

Power up

Settings > AirPlane Mode OFF, Do Not Disturb OFF

If not successful, an appointment at the Genius Bar of an Apple store is usually in order.

Apple Retail Store - Genius Bar

Then

Does the iOS device connect to other networks? If yes that tends to indicate a problem with your network.

Does the iOS device see the network?

Any error messages?

Do other devices now connect?

Did the iOS device connect before?

Try the following to rule out a software problem:

- Reset the iOS device. Nothing will be lost

Reset iOS device: Hold down the On/Off button and the Home button at the same time for at

least ten seconds, until the Apple logo appears.

- Power off and then back on your router

.- Reset network settings: Settings>General>Reset>Reset Network Settings

- iOS: Troubleshooting Wi-Fi networks and connections

If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network

- iOS: Recommended settings for Wi-Fi routers and access points

- Restore from backup. See:

iOS: How to back up

- Restore to factory settings/new iOS device.

If still problem and it does not connect to any networks make an appointment at the Genius Bar of an Apple store since it appears you have a hardware problem.

Apple Retail Store - Genius Bar