Confluence Server Log Files
Confluence has a tool for getting the server log at General Configuration > Troubleshooting and support tools
Follow the prompts to create a Support Zip. See Create a Support Zip for full instructions (or just use our Log Downloader app and get the log with one click).
When downloading the log files you do not need to include anything except the Confluence application logs unless support requests something else.
See Confluence documentation for Configuring Logging for adjusting the logging level (INFO, DEBUG, etc.)