How do you research an idea for writing a novel that is not already published?

Put your “idea” in question format and throw it at an online search engine.

Then take the results into consideration while deciding if it would offer any potential for a story of any kind, or simply add background flavor or authenticity to it.

A quick “G” search (Google is NOT a verb) came up with this link:

50 book ideas for writing a book you can start today