I don't believe it's actually exposed via the Reporting API like the accounts, summary and other reports are. I've tried every name I can think for it and haven't been able to retrieve it.
I'd really like to be able to programatically retrieve this as it would simplify the process of getting an entire domain (or org) on 2SV. All users could be added to an exclusion group, comms could be sent and a script could run each night that would pull the 2SV report and remove anyone who's turned 2SV on from the exclusion group (thus forcing them to keep 2SV on).
As it is, I have to manually login to CPanel, download the latest report and diff against group membership. I hate manual processes :-)
Jay