I don't quite understand the question. For an arbitrary solid body, there is no point on or in the body that would be considered the "origin". Each body would have its own "center of mass"; perhaps that is what you are looking for?
When creating a block feature, you can use the "origin and lengths" creation option. This arbitrarily defines one of the corners of the block as the "origin". The other block creation options do not specify an "origin" point.
For extrude features, there is no well defined "origin" point.