I intend to use tokens to access secured service in my app and question is do I need one token for all data stored in our organizational account or a separate token for each service layer?
A token is linked to your organizational account and to the URL of the app, so it will work in that app for all services accessible by that account.
This post may provide useful information for you. The executive-dashboard app from Esri's GitHub site is an example of accessing private services for a private or public app.
