There are two types of device comments: "global device comment" and "local device comment".
Device comments can be displayed in the ladder editor and Zoom editor windows.
Select [View] -> [Comment] from the menu to display the comments.
When setting both global device comments and local device comments,
select [Tool] -> [Options] -> [Program Editor] -> [Ladder/SFC] -> [Comment] from the menu to set
[Reference/Reflection Target for Device Comment].