How to complete the free development daily challenge task and earn points?

I am assuming you are referring to the free development days in the Clash of Zones events (Sundays during most weeks and Saturday/Sunday during warm-up weeks). On these days you can select the event you want to do as long as you do it before the day starts.

Check 'What is the clash of zones' for details how to do this.

If you don't select an event to do there will be a default event activated. To see what the event is open the clash of zones event screen and check the 'Today's Event' page for the requirements to earn points that day.