I was unable to run your model, but according to your post, I think you need to calculate the distance of the orders to the operator. If this is the case, you need to define the location of the order in the warehouse when the order is generated. I have attatched a simple model where each order has three attributes: (a) order's location in the warehouse, (b) the distance between the operator and the robot, and (c) the order serving time which is proportional to the distance. You can calculate all of these upon entity generation or upon entity entry into the Entity Server.
In the attached model, I assumed that the operator is located at coordinates [0,0,0] and the location of the generated order in the warehouse is a random triplet [x,y,z] in the range of [1,1,1] to [5,5,5]. I calculated the distance using vecnorm function, which calculates the Euclidean norm. I also assumed that it takes 2 seconds for the robot to travel 1 in the warehouse. You can customize these assumptions to match your problem. The model also outputs the attributes, which is accessible via the variable out.SimOut in the base workspace.