Shortcuts:
Shift + Command + L: Show Library.
Shift + Command + M: Show Media Library.
Xcode 10 has added a toolbar button to access the Object Library.
From a thread on Apple Developer Forum:
Library content has moved from the bottom of the Inspector area to an overlay window, which can be moved and resized like Spotlight search. It dismisses once items are dragged, but holding the Option key before dragging will keep the library open for an additional drag.
The library can be opened via a new toolbar button, the
View > Libraries
menu, or the ⇧⌘L keyboard shortcut. Content dynamically matches the active editor, so the same UI provides access to code snippets, Interface Builder, SpriteKit, or SceneKit items. The media library is available via a long press on the toolbar button, theView > Libraries
menu, or the ⇧⌘M keyboard shortcut. (37318979, 39885726)