In SAP JAVA system with multiple instance and multiple server nodes, its difficult to collect logs or check various default trace files/folders , specially when your diagnostics is for a single user. With the following documents one can get the information about the server node/instance where user is logged on.

How to get the server node information

1.Execute following command in the user browser where the user is logged on (execute it in the same browser window).

         javascript:alert(document.cookie);

 2. You will get similar pop up like belowthis gives you the node ID where user is currently logged in.

Reference:

http://help.sap.com/saphelp_nw04/helpdata/en/5b/ac1a0a8b8d6b4da3b79a7fe0aeabd8/content.htm