The Data360 Analyze API documentation can be found in the integrated Help for your system in the 'System administration' > 'API developer documentation' topic.
It is also available online for the latest version of Data360 Analyze here:
https://d3sa-preview.infogixsaas.com/docs/dist/help/Default.htm#j-admin/api-documentation.htm
However, I am not aware of any API that would enable you to download data files (i.e. the intermediate data that is present on the output pins of nodes or results data files saved to the Public or your 'My Folder' data directory) on the Analyze server.
Your data flows could 'push' data to another system using, for example, the SFTP, AzureBlob, Google Cloud Storage, S3, etc nodes.