FieldEdge syncs all data directly to and from NationBuilder via the mobile device it's installed on, so for that reason, we don't have an API.
NationBuilder itself does has a Public API that provides access to all of the same data FieldEdge does. You can find the documentation here: https://nationbuilder.com/api_documentation
For a "No Code" solution, please take a look at NationBuilder's integration with Zapier: https://zapier.com/apps/nationbuilder/integrations
The FieldEdge team is well versed in NationBuilder's API and Zapier so if you have any questions at all, please reach out and we'd be happy to help :)