I in an act of clumsiness I pulled off the cables connecting the reset button of my Super Snapshot V5 and the PCB. I asked Twitter and Mastodon for help, but to no avail. The search engine of my choice also did not come up any helpful link. Luckily information about the Commodore 64 is all over the web.
After taking a look at the expansion port of the C64 and tracing the soldering point which was still connected to a cable to line C (Reset), it was likely that what the Super Snapshot used to trigger a reset was lines A (GND).