How can one identify if FK's needed to be indexed apart from the NC indexes already residing
There are benefits to indexing foreign keys as they provide better join performance as described by SQLSkill's team here and here.


  It is generally recommended to create an index which leads on the foreign key column(s), to support not only joins between the primary and foreign keys, but also updates and deletes. 


A script can be found here or Indexes Supporting Foreign Keys.

Review any index recommendation that the scripts give and make sure you dont end up created a lot of indexes since there is always a cost of maintaining them.

Also, make sure that your FK's are trusted.