can i use usb otg in my ipad air2

No.

Hi

Iphone/ iPad do not use usb the only way to connect is Bluetooth / or wireless .

Cheers

Brian

Why apple dont support otg? It useful way to transfer file.

Because they don't.

No one here can address any question of "why" Apple made the design decision they did.

Ok i understood. Apple did. No matter the user experience and ease of use...