how can I see on which firmware my spark is running?
you can add in a Spark.variable() and set the version number in code to check it via an API call.
This feature might be available in future where polling for the core should give you the date and time that the firmware is flashed.
Do you mean (1) the version of the firmware with which your user code is linked? Or do you mean (2) the version of your own application code? I ask because “firmware” means different things to different people, and the “correct” meaning is counter-intuitive to many who have not worked extensively with microcontrollers.
If (1) then the IDE settings page says what you’re “building with” (which I think should be phrased “linking to” - you’re building one executable to be flashed to the Core).
If (2) then it’s @kennethlimcp’s answer.