[user02934123123]

This one can take slightly longer to find: it's not in the Forum Options area, but is in fact a usergroup setting (which is good: it allows you to set the ability to see who's left reputation comments at the usergroup level, so - if you wish - some groups can see this information, others can't).

Go to: AdminCP > Usergroups > Usergroup Manager

Then select Registered Users or whichever usergroup your registered users fall into. Edit this usergroup, and scroll down about two-thirds of the way to User Reputation Permissions. In this section there is a setting (the first) called Can See Who Left User Ratings: set this to 'Yes', and users in that usergroup will then be able to see who left them reputation/comments, via their UserCP (assuming you've left the UserCP template similar to its default; i.e. not removed the conditional column heading that allows for this).