In Splunk, the webhook Alert action accepts a single endpoint value to which to send the webhook. If you create an alert, then you can view it in Settings->"Searches, Reports, and Alerts", click the "Edit" dropdown, then click "Advanced Edit", then scroll down to the fields of "action.webhook". Here you can specify more settings for your webhook.
As for sending a webhook for Akamai, do you have documentation describing what the webhook should look like? If I understand correctly, you would like Splunk to have an alert which sends a webhook to Akamai that contains an IP, from a field in the alert.
