https://www.theverge.com/2018/10/30/18019194/apple-ipad-pro-2018-no-headphone-jack-lightning-dongle-adapter

Like it or not, Apple is removing the headphone jack from the new 11-inch and 12.9-inch iPad Pros. If you want to use a 3.5mm audio jack with one of the new models, then you will need one of Apple’s USB-C to 3.5mm dongles. That’s right: the new iPad Pro moves from a Lightning cable to USB Type C.

Apple’s removal of the 3.5mm audio jack from the iPads wasn’t without warning. The company has been removing ports from its lineup for a while now. Apple removed the audio jack from the iPhone 7 / 7 Plus, then removed all other ports except the audio jack and USB-C on the MacBook Pro and Air lineups. Apple is also increasing the number of dongles they sell, by introducing a $39 SD card to USB-C dongle for users who want to edit photos straight from their camera while on-the-go.