When a place asks for a cumulative GPA do you include all coursework taken at all universities (e.g.: do a weighted average of the unique units of coursework you did at Junior College + University), or do you only use coursework at your most recent institution, or do you report two or more cumulative scores where you can and then fallback on a different method when you can't.
If you are asked to self report (seems weird to me) and don't have a way to provide a full explanation then you do what you can. Some type of average weighted by credits. You are likely expected to consider post-secondary education only unless it is for admission to undergraduate programs or scholarships for such.
But, you should retain the details of the computation and how you arrived at the number in case you are ever questioned. This is especially the case if you have attended more than one institution.
But, I doubt that they are looking for only the most recent institution unless they say that. More likely they want a "complete" picture. If that picture isn't very flattering you will need to explain it, but don't leave things out.
If you produce other materials than just what fits on a form, you can, perhaps, include the GPA computation. Then, if there is any question, they can give you better instruction on what is needed.