Where are downloaded movies stored on ipad air

if your ipad is a newer version which has an app called apple tv

then you click that

and when it starts

you click on the tab control item in the bottom of the screen named library

when that presents you with the context content menu for library

you choose (click) on the item on the screen with the text Downloaded on it

that should provide you with a new content screen listing the media synchronized from your computer to your ios device

if it's a newer ios version then in

appletv app->lib->downloaded