In AD, there is one attribute that contain a value of Head of department in that attribute

How to fetch this department head field programmatically ?

Hi,

you can use REST API Url "http://siteurl/_api/SP.UserProfiles.PeopleManager/GetMyProperties"

and 

http://siteurl/_api/SP.UserProfiles.PeopleManager/GetPropertiesFor(accountName=@v)?@v='domain\username'

If you have Head of the Department attribute in your AD and it has been mapped with User Profile Service,you can able to see this attribute with value.

You have to extract this values in JavaScript and show it on app or page.