To see the filename with the extension:

Select the file in the Finder.

Choose File > Show Info.

Click the Name & Extension disclosure triangle to see the extension.
Mac OS X uses filename extensions to identify file types. AppleScript and Script Editor work with files that use the .scpt or .scpt extension.
Extensions may be hidden so only the file name is displayed in the Finder.
Select the file in the Finder.
Choose File > Show Info.
Click the Name & Extension disclosure triangle to see the extension.