Facebook allows users to hide their friends list, but there are still some methods you can use to discover the hidden list.
A remnant of the late Graph Search allows us to find mutual friends of 2 profiles, provided that at least one of them has a visible list of friends. (How to Find Mutual Friends of Two Facebook Accounts)
We now can use this method to uncover most of the hidden friends list of a profile.
By exploring our target’s profile, we should find users who liked or commented on his public posts or photos and check if their ‘friends list’ is visible. If so, will use the mentioned method to discover the mutual friends of these 2 profiles. We can later iterate this process, and apply it to our target and the friends we’ve found in the last iteration.
Save the friends you find into a table, and check the mutual friends of each of them with our target. You’ll find most of his friends list!
More techy users can automate this process, using a code from GitHub