Q. How do I cite a source in Chicago style that I found in another source?

Whenever possible, obtain and cite the original source.

Author-Date Style

Provide the original author and date in the text, and cite the secondary source in the references list.

See section 15:56 of the Chicago Manual of Style Online for examples.

Notes and Bibliography Style

List both the original and the secondary source in the note, but only the secondary source in the references list.

See section 14.260 of the Chicago Manual of Style Online for examples.