Security of HTTP proxies

If POST requests are being made to a website via a browser using an HTTP proxy from sslproxies.org, is it possible to trace the origin of those AJAX requests without having access to the proxy being used? Assume the role of the webmaster here, and assume the proxy used is either 'Anonymous or Elite Proxy' as marked on sslproxies.org

As a security project I'm looking at seeing if it's possible for me, the webmaster, to trace POST requests made through an HTTP proxy.