This information is available from a DBUTLTY RXX report.
Since CA Datacom version 11.0, the security user ID has been part of the log record and can be reported on by running DBUTLTY with the following:
The security userid is in the SEC.USER column of the report.
The security user ID is also part of the READRXX fields for a user written program to read the RXX file. The field is RXX-SECURITY-USER-ID.