There are 3 ways:
- Use Audit Log REST API: https://www.dynatrace.com/support/help/dynatrace-api/environment-api/audit-logs/get-log/
recommended solution if you are interested in a given environment auditing
- Use Audit Log UI in CMC (if you want to see in UI all log ins to the cluster)
- Process all nodes `log\server\audit.users.x.x` log files to have a complete view what happens with log ins/log outs.