How to obtain the value of the Nodal Volumes in a model?

In a thermal Analysis like SOL 153/159, temperature is the output at the node. Please clarify your question in more detail. What kind of output is being requested?  

Usually Volume is calculated for a solid. Area can be calculated for a Surface. A node does not have any Area or Volume. Please clarify in more detail to assist you better. 

Hi, when you do an analysis in FEM there is a concept called nodal volume or nodal area. It refers to the volume or area associated to a node depending on the elements connected to a node, so whenever you apply a temperature or a heat in a surface, the amount of that value that the node is seeing depends on if it reaches its area/volume. You could also translated it as a "weight" of the node when you do the simulation

When applying flux type loads or boundary conditions to nodal points, the units will still be those of a flux, i.e., loads per unit area. Patran’s input data forms for thermal loads and boundary conditions require you to specify an associated nodal area.... 

As seen in above image you want to apply a Heat Flux to a Node. Flux= Load/Area. That is why it asks for the Nodal Area. If you switch the option to Nodal Source, it will not ask for Nodal Area. See image below. 

The same concept applies to Convection -> Type Nodal. 

For nodal loads and boundary conditions, the nodal area must be defined explicitly.The Nodal Area Appears only when the LBC type is Nodal. It defines the area
of a boundary surface associated with the node.

So there is no way that Nastran can provide me with the value Nastran has calculated for the nodal volumes or nodal areas? I mean, in some step of the calculations it has needed to determine the nodal volume or nodal area when I provide a boundary condition of temperature in a surface, in order to associate that temperature to its corresponding nodes

Nastran is expecting this values to be provided by the user. This is an input to the code. We can call it user input.