.reqlog is the request log for a specific Endeca data store. By default, these logs are stored in the endeca-server\logs directory.
Studio
See Logging for StudioThe default location of eid-studio.log is the root directory of the WebLogic domain. ie /u01/app/oracle/product/Middleware/10.3.6/user_projects/domains/endeca_studio_31_domain
Support
Error contacting the Endeca Server
[oracle@Exalytics-01 ~]$ endeca-cmd create-ds staffing
Error contacting the Endeca Server localhost:7770: com/endeca/opmodel/opSupport/MkMdexRunner
caused by:
com/endeca/opmodel/opSupport/MkMdexRunner
caused by:
com/endeca/opmodel/opSupport/MkMdexRunner

Just restart the Endeca Server