Philosophy asks the really big questions, such as what is goodness? what is reality? So  pretty much anything could be relevant to philosophical research. But there are several places to look to find specifically philosophical approaches to topics. Philosophers mostly read and write:

• books, which offer extended original presentations of, or critical analyses of, broad philosophical ideas and systems
• articles and essays, typically providing either a detailed critique of a narrow, focused topic or question; or a short summary of a broader idea