It's hard to tell exactly what you're doing, since you're copying plain text instead of InputForm, which would be more helpful, but it looks to me like you're a) not using any correct syntax to request a property value and b) somehow also including the "Word" type entity "region" instead of the "Region" property associated with physical systems. Any of these will get you what you want, I think:

(Local2) In[5]:= 
Entity["PhysicalSystem", "RectangularBarMagnet"]["Region"]

(Local2) Out[5]= Cuboid[{-(QuantityVariable["a","Length"]/2), -(
   QuantityVariable["b","Length"]/2), -(QuantityVariable[
   "c","Length"]/2)}, {QuantityVariable["a","Length"]/2, 
  QuantityVariable["b","Length"]/2, QuantityVariable["c","Length"]/2}]

(Local2) In[10]:= 
Entity["PhysicalSystem", "RectangularBarMagnet"][
 EntityProperty["PhysicalSystem", "Region"]]

(Local2) Out[10]= Cuboid[{-(QuantityVariable["a","Length"]/2), -(
   QuantityVariable["b","Length"]/2), -(QuantityVariable[
   "c","Length"]/2)}, {QuantityVariable["a","Length"]/2, 
  QuantityVariable["b","Length"]/2, QuantityVariable["c","Length"]/2}]

(Local2) In[6]:= EntityValue[
 Entity["PhysicalSystem", "RectangularBarMagnet"], "Region"]

(Local2) Out[6]= Cuboid[{-(QuantityVariable["a","Length"]/2), -(
   QuantityVariable["b","Length"]/2), -(QuantityVariable[
   "c","Length"]/2)}, {QuantityVariable["a","Length"]/2, 
  QuantityVariable["b","Length"]/2, QuantityVariable["c","Length"]/2}]

(Local2) In[9]:= EntityValue[
 Entity["PhysicalSystem", "RectangularBarMagnet"], 
 EntityProperty["PhysicalSystem", "Region"]]

(Local2) Out[9]= Cuboid[{-(QuantityVariable["a","Length"]/2), -(
   QuantityVariable["b","Length"]/2), -(QuantityVariable[
   "c","Length"]/2)}, {QuantityVariable["a","Length"]/2, 
  QuantityVariable["b","Length"]/2, QuantityVariable["c","Length"]/2}]