How to display full path to file in spotlight search?

If you want to view the path to the file directly in the spotlight search you can simply hold down cmd ⌘:

Without cmd ⌘:

With cmd ⌘:

When Spotlight is selected from the Menu Bar, the window does not show the full path, as shown below.

However, if you select Show all in Finder..., then the full path is shown in the Path Bar at the bottom of the Finder window. In the image below, the full path is shown as ~/Desktop/Dave.txt. If there is not enough room to display the full path, then the full path can be read by placing the mouse over the text. Also, any part of the path (including the full path) can be dragged and dropped into a text window.

If you need to preview a document in the Finder window, the highlight the file and press Cmd-I, as shown below.

When Spotlight is not being used, the Path Bar in the Finder window can be toggled between hide and shown by pressing Opt-Cmd-P. You can also select Hide Path Bar or Show Path Bar under View in the Menu Bar.