Can someone help with this request?
No idea; doubtful that it is possible. I was thinking you could look up every user in the system and check their individual preferences but I don't think this field is available via the API.
Non API related ideas:
Maybe try contacting support to see if they can find this information for you? There is likely some backend scheduled function (lamda?) that pulls a list of all subscribers for each news digest. Try "hacking" into that and seeing what it calls.
I don't think this information is available in the Jive REST API and setting this notification preference is not available from the Data Export Service.
If you're on Hosted or On-Premise, you can query the database. If you're on cloud, there may not be an option.