Uber Suggest was a tool that allowed you to check out and see what drop down terms in Google's Autocomplete populate with. Now that tool is gone (I think Neil Patel bought the domain but I'm not sure) there is a new one from Joe Hall that popped up called Term Suggest: https://termsuggest.com/ it allows SEO experts to research all of the drop down suggestions and what terms you can target.
Another great tool is Surfer.