You probably are referring to the ULOGPFX environement variable. If you have not set it for your client
it is probably set in the registry. By default on installation I bellieve it is set to "%TUXDIR%\ULOG"
Here is a good starting point for the Tuxedo 6.5 Workstation client documentation:
ULOGPFX is an environment variable. Your client executable can set an environment variable as part of a startup script,
it can be included in a file used by the client that is defined with WSENVFILE environment variable, it can be read in
a file by the client executable after startup using the tuxreadenv() API, it can be set by the client using the tuxputenv() API,
the profile for the user executing the client can have an environment variable defined, or the windows registry can include
a definition for the environment variable(there is also an BEA applet on Windows for administration but I think not on client only installs).
WSNADDR is an environment variable that defines the address of the workstation listener that the client will connect to.
Look for where your client defines WSNADDR and add, or modify,the ULOGPFX definition to meet your needs.