Riddleform and Hadana's Climb
Yes, your Riddleform will keep the +1/+1 counters on it.

Permanents don't generally care what counters are on them unless they have and effect that says they should care. So even when your Riddleform turns back into an an enchantment it will still have it's +1/+1 counters on it (even though those counters won't do anything). 

One special case to note is that your Hadana&#39;s Climb can only place +1/+1 counters on creatures. So even if your Riddleform has already received a counter or two, you will not be able to place additional counters on it with Hadana's Climb (and then cause the transform) if it is not currently a creature.