How to get lap length, speed, cadence, power and elapsed time for a data field?

You should find the info here: The class to look out for is Activity
https://developer.garmin.com/downloads/connect-iq/monkey-c/doc/Toybox/Activity/Info.html

use Activity.getActivityInfo() and you should be able to get what you need.

Use Activity.getActivityInfo() and you should be able to get what you need.

Thank you for the quick reply. I am aware of that class and I can derive current, average and maximum values for the whole activity. I just don't know how to derive them for LAPS.

Thank you. Do you think this would be ok:
onTimeLap (get elapsed time and distance)
compute (avgLapSpeed = (elapsedDistance-onTimeLapDistance)/(elapsedTime-onTimeLapTime)
Should I add any more onTime events?

That should work. You might want to make a few enhancements...

• save the onTimeLapDistance and onTimeLapTime values in onTimerStart in case onTimerLap isn't called when the activity recording starts.
  
• add some null checks to avoid crashes if the onTimeLapDistance and onTimeLapTime aren't initialized when compute is called.
  
• guard against divide by zero in case compute is called before any time has elapsed.
  

you have to do a bit more work if you want to calculate lap averages (average power for the lap for example).