`SMTNodeData` is the right command for those questions.

1) `SMTNodeData["at"]` returns all nodal DOFs.
`SMTPostData` command is for visualization and in general can smooth fields to have nice plots.

2) Global tangent matrix by its definition includes only true unknowns of the problem. If you want an extended tangent with all nodal DOFS included then you can do something like this
```
tmp = SMTNodeData["DOF"];
(*unconstrain all DOF*)
SMTNodeData["DOF", tmp /. -1 -> 0];
SMTSetSolver[];
Kall = SMTData["TangentMatrix"];
(* return all back as it was*)
SMTNodeData["DOF", tmp];
SMTSetSolver[];
```

This will not have any side effects.