How to reference studies mentioned in a paper without having to read the original papers? I'm review the literature at the moment. Now I'm reading a paper that mention other studies. How can I reference them without reading the original papers?
Let us assume, for example, you read Doe (2011) and find Smith (1966) referenced therein. Technically, you can say something like "Smith (1966, cited in Doe, 2011)", or alternatively "(Smith 1966, cited in Doe, 2011)." The exact format depends on the format of the journal (it is also possible to phrase it "cited by" instead of "cited in").

That said, however, it is very dangerous to provide such quotes since you do not know if the person(s) citing the paper has understood it correctly. It is not unheard of that people cite for very odd reasons and not double-checking works cited may just propagate such errors. 

So, it is possible but not recommended.