This might be a stupid question to ask here .i am confused whether the dof of this drone is 3 or 4?
In general i would say there is not enough information on this drawing, so we all ASSUME.
If you look at this and assume it is a multicopter with 2 counter rotating propellers (can not fly in a normal fashion without a pivoting mechanism, like a Chinook) you can only have yaw, roll and up down control which makes for 3-DoF. For the arm it give you 2 DoF (assuming no other pivot point exist that are not visible on the drawing)
From a practical point of view if the top is really a drone (multicopter) then it needs four propellers (which i can only see two of in the 2D picture)
A multicopter like i assumed moves like a ship 6-DoF (not an airplane 3-DoF)
I argue that as far as the drone is concerned it still has a 6-DoF. The attached arm has 2-DoF. wikipedia
Whether it serves any purpose to count the additional movement the arm can make as additional DoF is in my view debatable because you can not move in any more ways than before (i look at the maneuverability from the drones perspective and the arm endpoint Pe). You achieve the same result for the endpoint of the arm when you move the drone or when you move the arm.
I could of course be completely wrong being human.