Absurdity aside, in thie specifc example Wikipedia doesn’t cite any sources.

The article (in English, anyway) is a summary of the plot of the book and there is not a footnote nor any external reference - and why would there be? It’s a summary of the plot, not a commentary or a critique of it. In this case, there’s no need to cite a source. https://en.wikipedia.org/wiki/A_Game_of_Thrones