Option 1
1.1 click hub ( because this is arcgis online, it is called hub, if you are in portal, it is called sites)
1.2 click manage
1. where to find open data site on arcgis portal
1.1 click site
1.1.2 click manage site
1.1.3 click site
Normally open data site is at content, apps, sites, since their type is hub site type.
However, due to some reason, its type could be web apps instead of hub site.
So if you can't find it at hub site, then just search content 'open data', should find it.
