I had 3 source: How does the built-in MQTT endpoint work?
Blynk message format: https://github.com/blynkkk/blynk-server/tree/master/client
And some debuging
In the source code I see 3 function, which may be interesting
i, reportingDao.process(state.user, dash, deviceId, pin, pinType, value, now);
this is may be for database handling
ii, session.sendToApps(HARDWARE, msg.variableHeader().packetId(), dashId, deviceId, body);
This is for app update
iii, state.user.profile.update(dash, 0, pin, pinType, value, now);
This I could not follow up, yet.