How can I tell which generation my iPad is?

Settings, General, About. The Model Name line says it outright, like iPad (9th generation), on anything running iPadOS 12.2 or later. If it's too old to show that, use the Model Number on the same screen: tap it and it flips to an A number, A1822 style, which is also printed in tiny text on the back. Apple's identify your iPad model support page matches A numbers to generations, and case listings use the same generation names. On updates: as of this year's release, roughly the 8th generation and newer still get the current version, older ones are on security patches only.