Subscribers have a little box on their page, listing everyone who they have marked as their friend in their deviantWatch settings, however, no matter whether they have it enabled, or even if you aren't a subscriber, you can always find out who their friends are by going to their deviantpage, adding "myfriends" to the end of the address in your browser's address-bar, and hitting enter. This is also an easy way for you to link to your friends - just check them as friends in your deviantWatch and link to the myfriends-page in your journal ^-^