The knowledge graph is Wikipedia, that they use under license, or other sources that they have paid for a license to use. What you're thinking of is "featured

The knowledge graph is Wikipedia, that they use under license, or other sources that they have paid for a license to use. What you're thinking of is "featured snippets". As far as I know, the justification behind those is that they are exact quotes that are followed by a citation (a link). Google argues those are fair use, since it's a properly referenced quote.