API keys are shown only once, immediately after they have been created. After displaying one time, for security reasons, API keys are stored using one way encryptions and therefore cannot be retrieved.
If you've forgotten your API key simply create a new one. Also, as a good security measure, you should disable the original API key that was forgotten.
API help page
Related Articles:
Does Smartwaiver have an API?
Why should I use multiple API keys?
