https://www.reddit.com/settings/data-request
Having worked at a company that had a massive influx of GDPR requests we weren’t prepared for, this one could actually cause them some trouble if Reddit don’t have that process properly automated.
Not that easy, it's not a simple SQL query: https://gdpr.eu/checklist/
If they give you some data under that framework, then it implicitly means that legally they acknowledge that they have checked all of those boxes. So before they give you the data there are probably lots of "are we incriminating ourselves by giving this guy this piece of data?" questions that they're asking themselves.