/sys$common/syshlp/helplib.hlb TELNET, Qualifiers, /LOG_FILE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /LOG_FILE=file

    Optional. Default: No logging.

    An optional log file that contains all session output. Using this
    option does not affect your terminal output. You cannot use this
    option for TN3270 sessions.