Asking your SMEs or product owners for information to populate a user guide and then waiting for that information is a sure fire way to never completing said user guide (unless you’re among the lucky tech writers to have SMEs/product owners who enjoy writing user documentation).
Instead, research the product and then write a first draft to the best of your understanding, even if it’s just headers. First drafts don’t have to be perfect. Send your SMEs/product owners that draft and ask them what you’re missing.
It’s far easier to critique than create.