1) A figure is not considered adjacent to itself, but is a figure considered adjacent to the space that it is occupying?

2) Is a massive figure considered adjacent to the spaces underneath it? Specifically, can a massive figure play Parting Blow when it steps on a smaller figure?

1) Generally, a small figure is not adjacent to the space it occupies.

2) As far as I know, a large figure is adjacent to all spaces it occupies, because you can choose another space the figure occupies for determining adjacency to another space. (Also, a Large figure is adjacent to a figure in the same space.)

So, a Massive figure can Push a figure and use Parting Blow.