Submit the following URL request to QuarkXPress Server. The returned will contain the subrenderer information.
http://servername:port/getprocessid
<PROCESSID>
<MASTER>
<ID>6096</ID>
<STATUS>BUSY</STATUS>
</MASTER>
<SUBRENDERERS>
<SUBRENDERER>
<ID>2844</ID>
<STATUS>FREE</STATUS>
</SUBRENDERER>
<SUBRENDERER>
<ID>1308</ID>
<STATUS>FREE</STATUS>
</SUBRENDERER>
</SUBRENDERERS>
</PROCESSID>