At this point I feel it's too generic the question.
If you talk about your own zombie pages/infected pages, is the same but the other way around. First update your systems, if using a CMS like WP check for tools that help you audit a little bit like
Sucuri, Patchstack or Wordfence.
If you think you have zombie pages is because you have found something that makes you suspicious about it, some evidence.
With that evidence, you should look be able to look for footprints, like a URL that is used to redirect or to link.
If you know how to use SQL queries you should be able to detect the infected content with JS or just outbound linking by querying a match of that footprint.
Otherwise, if there is a CMS like WP again, there are tools like
Better Search Replace that help you find this with a simple interface.