I am reading the literature review of an article and the review article mentioned that the second article found positive relationship.
Now, should I cite both or just the second article that found the positive relationship?
You should cite and read the older article that shows the finding. Referencing articles through somebody else's publication should be avoided at all costs. the reason is simple. When you reference a fact through somebody else's work you are also unwittingly citing their interpretation of the original work. There are examples of misconceptions that have been born and carried through many publications because the original have been misinterpreted or misrepresented by a citing author and from which other have sourced the information.
If no other options exist then citing the work as, for exampe " X (yyyy) cited by/in Y (yyyy)" or "(X, yyyy, cited in Y, yyyy)".