Is there a heuristic to determine whether a method or field belongs in a class?

Look at the SOLID principles. Those will give you guidance on where a method belongs.

I'd be inclined to make List(Of Employee) into its own class at this point, so that it can have its own method AddSkill().

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.