Sharepoint - Where to get a product key for trial?

The key is in the same page under the GET STARTED NOW button -

"Installation requires the following product key: "NQTMW-K63MQ-39G6H-B2CH9-FRDWJ

Cheers

Be careful that if you wan to test SharePoint Standard you'll need a purchased key as currently, Microsoft is only providing an Enterprise trial key (which is NQTMW-K63MQ-39G6H-B2CH9-FRDWJ) and no standard trial key. Happy testing !