I have already searched in the shortcuts in the Xcode preferences but I couldn't find a way to get it back.
My current interface:
Click the "square in a circle" button at the top, left of the "show standard editor" button. Alternatively, use "View > Libraries > Show Library" or hit Shift-Cmd-L.
来源：https://stackoverflow.com/questions/52566356/my-library-pane-is-missing-how-to-get-it-back