You can see all the list of reason codes under configure Chargebee -> reason codes.
If you would like to export subscription data to see the various cancellation reason, you need to perform an export of the subscriptions you want. From there you can look at the canceled reason. You can do this by going into the subscriptions tab, applying the desired filter, and then exporting the subscriptions.
If you are using API, then please refer to this link to know more about export subscriptions with reason codes.