does the 9th generation ipad support wireless charging?

No. See the following from iPad 10.2-inch - Technical Specifications - Apple

• Charging via power adapter or USB-C to computer system

No iPad support wireless, magnetic charging. None.

To have wireless charging a device needs to an electrical isolator, like glass, in conjunction with a magnet,used in the back of all the more recent iPhone models and all Watches.

Currently, all iPads have an all aluminium back case/chassis with no electrical isolating glass to have and safely use wireless, magnetic charging.

Sorry.