Where isHeadphone plug on new iPad Air

There is no 3.5mm headphone jack. You can either use headphones that have a lightning connect that plug into the lightning (AKA charging) port or you can use Bluetooth headphones or you can purchase an adapter that plugs into the lightning port that has a 3.5mm jack on the other end.

Its gone.

You purchase an Apple USB-C to 3.5mm audio adapter and use the USB-C connection for headphones now.

https://www.apple.com/shop/product/MU7E2/usb-c-to-35-mm-headphone-jack-adapter?fnode=1d7ffdcc2f2c2ffe5a4ccf4fdf3ec44d90c654ce649445f48e6ee00604dd9bdb5efc3ec7fe3d4e0d803a95c6fddf2384668568ffb438196988daf77564a484c7a3acaef2cd7b38cee72a1d4276e4a04005483df8cf9ff21613865e61f6b4ca1a

OR

You use wireless, Apple Bluetooth AirPods or other third party wireless Bluetooth headphones, ear buds.

Best of Luck to You!