How can i restrict non friends commenting on my cover photo ?

[Rajesh]

You need to do the following. Go to your facebook,
click photos>Albums>Profile pics>select the pic you don't want people to see, then click on edit and a window will popup there you can add description, put a location, etc next to where it says
"Done Editing" there is the audience to for the pic, click and select only me. Unfortunately facebook doesn't allow you to change the setting for the whole album. You can alternatively block everyone from ever commenting on your timeline.