Final answer:
In a Studio Session, usually anyone with access to the document can edit an existing markup, but permissions may vary based on the session creator's settings.
Step-by-step explanation:
In a Studio Session, the capacity to edit an existing markup depends on the permissions set by the session creator. Generally, the correct answer is B) Anyone with access to the document, as Studio Sessions are usually collaborative and allow all participants to make edits unless restrictions are specifically applied by the session creator. However, it's important to note that permissions can be customized, and in some cases, only certain users may have the ability to edit markups or the session creator might limit editing capabilities to users with specific privileges.