hey, cm, you´re playing guitar now? [:D]
Paw, I´m not sure I entirely understand your questions.
Basically you seem to be a bit lost what this guitar symbols are about.
They are more or less suggestions how to accompagny the piece. So here the composer suggests playing a Cm9 chord and to help the guitar player he shows the fingering of that chord. The beginner may take this chord and play it in an appropriate rhythm all over the bar. The more advanced will do something else with it. Not necesseraly following the melody, it´s usually an independent accompaniment arranged by the guitar player in advance or right during playing.
What´s very confusing in your post is your usage of the term "key". Although a key is a single "switch" on the keyboard, in musical language it describes the overall tonality indicated with the accidentals in the beginning of the stave. You should better use "pitch", or more general "note" for better understanding.
(But maybe that´s because of my mediocre english.... [8-)] )
Generally once again an attempt for an answer: The most important indication is the Cm9, this tells you what harmony you should use in that moment. What you do with it is up to you. And still that is not entirely obligated, Jazz history is full of versions of the same piece harmonized differently.
Maybe ask your question a bit more specific if that didn´t help,
bests,
- M