How could i get the n-th node of a way in Overpass?

Firstly, sorry for the bothers.

I am a beginner programming with overpass. I would need to get a query which allows to obtain the n-th node of a given way. I know i should use evaluators for pos and ref but i do not know how to make this query. i do not understand the use of pos and ref in the evaluators.

Please, could anyone to help me?

Thanks a lot !!!!!