Shurgs??
 

should shrugs be done when working the shoulders or back. When I do dumbell shrugs I feel it more on the back of my shoulders.

Guys do them both ways, I do them on shoulder day. There's no way I'm doing shrugs after doing back.

I look at things alittle differently than most. I've done them on both days and this is how I view them:

Shoulders day: Doing side laterals warms up the traps to a small degree. Your forearms are also well rested for holding alot of weight. I like to do 4 sets as my next to last exercise. My last exercise is rear laterals which will torch the bottom of your traps to a small degree.

Back Day: Again, your traps will be warmed up because of the barbell/cable rows. Also deadlifts will effectively torch that area. I don't recommend doing them on back day because:
-Your forearms are really burnt out from grasping alot of weight on all consequent back lifts. (pulldowns, rows, ect.)
-Doing deadlifts on back day works the traps very hard anyway.
-Your lower back should be very fatigued from doing barbell rows; or any rows for that matter. It might result in you doing less weight for your shrugs...Which won't benefit you.
-Finally, if you try to compensate by moving shrugs to the middle of your back workout, your forearms will be very weak after doing them, limiting you from using heavier weight for the remainder of your workout.