The breadcrumbs in the top-left corner of the document view show where the open item sits in the project. The first crumb names the section you are in (Items, Baselines, Reviews and so on) and takes you back to its list; the crumbs after it are the parent items, ending with the open item.
Click any crumb to open that item. Right-click a crumb to copy the item's ID to the clipboard.
An item can have several parents. In that case an up-down arrow appears after the breadcrumbs; click it to see the other paths under Also in and jump to any of them. A path shown as Root level means the item also sits at the top level of the project.
When a path is longer than three levels, the middle crumbs collapse into a ... button. Click it to see the full path. Long titles are shortened; hover a crumb to read the full title.
Baseline and review pages use the same bar to show the baseline or review you are in.