Whom to cite from an article: the reporter or the person who provided a quote to the reporter?

To add to Allure's suggestion, I think it would be most appropriate to make a slightly longer citation like

According to (Corak, reported in Younglai 2016)

You stated that you didn't want to include both names, but I think it is more helpful to the reader that way. Additionally, the above citation tries to be not too wordy (compared to yours), as it is just a footnote inside the parentheses rather than disrupting the flow of text.

The ideal, of course, would be that you find a paper originally published by Corak or some other academic that identifies this phenomenon (the "theory/concept" you mention), but you may not have the time to do a detailed dig through the literature.

Since you did not interview Corak and have no firsthand information on what he actually said, you must cite Younglai.

If you had access to a reliable transcript of the interview, and verified there that Corak said what Younglai claims he said, then you can cite Corak.

If you absolutely must reference this, @6005's solution seems like the best approach. However, I suggest that you find a better source instead.

The major purpose of citations is to direct the skeptical or curious reader to sources supporting an argument. Referencing a newspaper article where someone restates the idea doesn't serve that aim. The other major purpose is to assign credit. This quote may just reflect a idea in the field, rather than Dr. Corak's innovation. Both of these goals are better served by citing better sources from the relevant literature. However, you can (and should!) do some digging to see if Dr. Corak has written anything relevant.

On the other hand, there a few situations where you might want to cite this instead. A major one would be to demonstrate popular support for—or at least interest in—the idea being discussed. In this case, the newspaper article is more relevant, though you might want to namecheck both, using the "reported in" or "quoting" formulation in the other answers.