When i have that enchantment in a creature that has double strike, when it attacks, do i put 1 or 2 counters in that creature?
Ordeal of Heliod
Just one +1/+1 counter.
"Whenever enchanted creature attacks" means when the enchanted creature is declared as attacker.
So , even the enchanted creature has double strike , you declare this creature as attacker just one time , Ordeal's 1st ability will trigger only once.
On the other hand , if Ordeal's 1st ability says "Whenever enchanted creature deals combat damage to a player".
So in this case , if the enchanted creature deals combat damage to a player in both 1st and 2nd combat damage step , the ability will trigger twice.
Please autocard , check it on [read this first] - creating a rules thread.
And use lower case c to autocard.