You can search the folder structure of portal installation under /usr folder. You should find the occurance's. Anyways here are the locations where I found the favicon.
./JCxx/j2ee/cluster/server0/apps/sap.com/com.sap.engine.docs.examples/servlet_jsp/_default/root/favicon.ico

./JCxx/j2ee/cluster/server0/apps/sap.com/com.sap.lcr/servlet_jsp/sld/root/favicon.ico

./JCxx/j2ee/cluster/server0/apps/sap.com/com.sap.lcr/servlet_jsp/sld/root/img/favicon.ico

./JCxx/j2ee/cluster/server0/apps/sap.com/com.sap.rprof.remoteProfile/servlet_jsp/exchangeProfile/root/img/favicon.ico

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How to change SAP portal favicon?