PSD - How to study documentation?

Think about whether the documentation is necessary for the team to complete their work. Might they provide a better and more creative outcome if they just collaborated instead? A user story, for example, is not a detailed document, but a placeholder for a conversation about a potential requirement.

Think also about whether documentation is necessary for work to be Done. User instructions, release notes, or some other kind of technical write-up may be needed if work is to be of usable quality, in which case it might reasonably be stipulated in the Definition of Done for the product.

Documentation in Scrum is just like documentation in any agile practice.  Do what is needed.  Scrum does not specify any kind of documentation other than that which is needed to effectively communicate the Product Backlog Items needed for a product.  Scrum also suggests that information be shared openly in order to facilitate transparency of the work being done or completed.  As @Ian Mitchell points out documentation is sometimes necessary for work to be completed.  The goal is to do all of that documentation but not spend time working on documentation for the sake of writing things down in case it could be needed at some point in the future.