Watch the documentary in 3 years? :) I've only got enough knowledge about the markets to be dangerous, so don't expect any of this to be complete and accurate.

I don't think this type of information is publicly reported; or really aggregated anywhere. The brokers whose clients sold short presumably know the clients positions, and the clients know their positions, but absent an aggregated report across brokerages of that, nobody would know the whole picture. A brokerage probably has a duty to keep their clients' positions confidential, however.

I don't know how securities lending is organized. If it's centralized around a single vendor like clearing and depository is; maybe that vendor would know when shares were borrowed and returned, and could guess about the positions. Similarly, brokerages with lending programs should know when their clients' shares were borrowed and returned and could have a partial picture. This may again be data the brokerage or the lending facilitators would have a duty to keep confidential.