The library pane moved in Xcode 10. Many developers were left confused.
To open the library pane in newer versions of Xcode, select the square within a circle icon in the top right hand corner.
This will bring up the library pane and you can search for any object.
Another option is to go to
View > Libraries > Show Library
The keyboard shortcut to open this library pane is Shift + Cmd + L.
If you want to library pane to stay open, you can use the keyboard shortcut Shift + Cmd + Option + L. This opens a persistent library pane window you can move into your desired position: