Lambda triggers for Cognito User Pools refresh token?

No, no triggers are fired on that event. The trigger on the UserPool are the following: Pre sign-up, Pre authentication, Custom message, Post authentication, Post confirmation, Define Auth Challenge, Create Auth Challenge, Verify Auth Challenge Response, and User Migration. A token refresh does not trigger any re-authentication, hence no triggers are fired. When the refresh token itself has expired, the user will have to re-authenticate, and the authentication related triggers will be fired.