Alright, I am able to retrieve http://[mycommunity]/restapi/vc/users/self/settings/name/custom_zendesk.username but how do I retrieve all the custom_zendesk values available?
Retrieving http://[mycommunity]/restapi/vc/users/self/settings/ doesn't show any custom_zendesk values. Neither does http://[mycommunity]/restapi/vc/users/self/settings/name
Please keep in mind that the response for the list of settings is paginated, so you'll need to page through it using the "page" parameter. You can also adjust the "page_size" up to 1000 in order to get more results per page.
Regarding the custom setting value you mentioned, it will only show up for a user if it was configured as user setting. If instead it's a node (community, category, board, etc) setting, you will need to make the call for the proper node. For example:
/restapi/vc/settings?page_size=1000
