You can set the path for sql_server.log using this keyword in ctsrvr.cfg:
The SQL statement diagnostic logging keyword has been added to the default Server config file, ctsrvr.cfg:
; SQL statement diagnostic logging
;SETENV TPE_LOG=<alternate path to sql_server.log>
This keyword is present in the config file, but it has been commented out for your convenience (so it is there if you need it, but it is NOT enabled).