You should always do your best to locate the original, primary source. But in some cases, such as when an original work is out of print, unavailable, or in another language, you may need to quote from a source you did not look at directly.
In your Works Cited list you will list the secondary source you used. In the text, you'll include reference to both the original and the secondary source.
EXAMPLE - Works Cited
Lacey, Sajni, and Arielle Lomness. "Better Together: Assessing a Leisure Reading Collection for an Academic and Public Library Partnership." The Journal of Academic Librarianship, vol. 46, no. 1, 2020, pp. 1-4. https://doi.org/10.1016/j.acalib.2019.03.011.
Narrative in-text citation: Diers and Simpson describe ... (qtd. in Lacey and Lomness 3)
If you are paraphrasing from an indirect source, you do not need to use qtd. in, provided you have made it clear in your text that you are using a secondary source (MLA Handbook, 6.77).
EXAMPLE - Doctoral Dissertation
Wang, Xiaozhu. New chelators for radiopharmaceutical chemistry. 2019. U of British Columbia, PhD dissertation. UBC Open Collections. http://hdl.handle.net/2429/69977.
Parenthetical in-text citation: (Wang 42)
Narrative in-text citation: Wang ... (42).