Hello,
Upon searching internally, I was unable to find how to implement Data Logger with Google IoT core which is most likely not supported. However, from this public article [1], it is said the following:
"Stackdriver Logging collects and stores logs. Key device lifecycle events are logged for auditing. A subset of telemetry events can be relayed into Stackdriver Logging for analysis and reporting. Using Stackdriver Logging can save you a lot of time and effort compared to building a custom logging solution."
I would encourage you using Stackdriver Logging