In FontLab Studio 5 for Mac, the Output panel has “collapsed”: only the top bar with the Close button is visible.
You can fix it manually. Go to your user Library/Application Support/FontLab/Studio 5/Workspaces folder, open the file CurrentWorkspace.rc in a plain text editor such as TextEdit. Find the string containing “196_Height” followed by a number and change the following number (the height of the panel) to some larger value, e.g. change “196_Height 10” to “196_Height 200”