How can you tell if people can accurately identify AI generated text?

If a person reads AI generated text and does not notice, they by definition will not know about it.

There have been numerous cases of people accessing human created content as being AI.

There are instances where it seems relatively uncontroversial that it is AI generated, but without knowing both the amount of AI content people are exposed toand the amount that they register I don't think you can draw a conclusion of the overall state.