How to disable ARC for a single file in Xcode 5?
Well, I just tried and found that you must had dragged the window to a smaller width. You need to drag it back to show the Compiler Flag column:
To fix the real issue rather than a GUI issue, select the file and press ENTER, then you can add the -fno-objc-arc compiler flag.
You appear to be missing the right-hand column. On my install it looks like this:
Notice the 'Compiler Flags' column to the right of the 'Name' column.
Double-clicking anywhere on the row allows me to type into the flags as long as that column is on screen. Making my window sufficiently thin causes it to be invisible so the first thing I'd try is making your window super-wide, to see whether you can get a flags column.