In a published research paper, the author has cited a thesis/paper, which is not available online. The question is, when I'm writing my paper and I need to cite the corresponding unavailable paper/thesis, what should I do? Should I cite the original material even though I haven't read it? Or the paper that cited the unavailable material, say in its literature review section?
Assuming X is citing the reference Y whose content is unavailable, it is fine to cite Y just as done in X. It is better to mention it as a secondary source by stating that the concept mentioned in Y is as claimed in X. @jakebeal's answer to this post is most apt solution for this problem.
Some sources may inaccessible or totally unavailable (as in your situation) but they are cited nonetheless in the conjecture that the content they are assumed to provide are true. For instance, if an important method was proposed long ago and you wish develop on it, you ought to cite the original author of the paper (in addition to the standard books you refer), even if you couldn't access the paper yourself.