You can find the CakeMail API documentation on the Dev Portal.
Example call to List.GetList:
var cakemail = require("cakemail-api-wrapper");
var client = new cakemail.Client({
apiKey: "<YOUR API KEY>"
});
client.execute("List", "GetList", {
user_key: "<YOUR USER KEY>"
}, function(err, data) {
console.log(err);
console.log(data);
});