Using the management API, you can fetch the picture property with the Auth0 Management API v2 or Auth0 Management API v2 endpoints.
Will get you the response:
{
"picture": "https://s.gravatar.com/avatar/55502f40dc8b7c769880b10874abc9d0?s=480&r=pg&d=https%3A%2F%2Fcdn.auth0.com%2Favatars%2Fte.png"
}