Go to the friend's profile you wish to view. Then, click Games which should be on the right side, above their list of friends. Should be current status, badges, Games, Inventory. Select Games, then select the tab that says wishlist (there will be a Recently Played Tab, All Games Tab, and various other tabs for things you may have done(wishlist follow, review)). When I view you there is no wishlist tab, letting me know you probably don't have anything in your steam wishlist.