https://wccftech.com/apple-selling-type-usb-c-to-3-5mm-adapter-for-ipad-pro/

Apple is slowly removing the 3.5mm audio jack from all its devices so it is hardly surprising that the new 11-inch and 12.9-inch iPad Pro slates don’t have one either. This began with the iPhone 7 and iPhone 7 Plus, after which the company removed all ports except the USB-C and audio jack on the MacBook Pro and MacBook Air series.

However, you can still connect wired audio devices such as speakers or headphones to the new iPad Pro models by using the new Type USB-C to 3.5mm headphone jack adapter, which will work like the Lightning to 3.5mm variants. The latest adapter is now available on Apple’s website for $9 and it can be used with the Apple’s USB-C notebooks too, though it is highly likely that you will not need them for those machines.