scan nodes in chef-automate compliance section without using chef-server.

How can I scan nodes in chef-automate compliance section without using chef-server?

You can use the remote scanning capabilities within Automate to scan via WinRM or SSH for regular servers and network devices (routers, switches etc.). You can set up a regularly scheduled scan job with the target parameters within the Automate UI. The compliance scans can be access through the Scan Jobs tab at the top. The scans also support remote scans of Azure and AWS environments.
The description above is for Automate 2. Automate version 1 has similar functionality but doesn't support scanning cloud environments such as Azure and AWS.
Automate 2 documentation: https://automate.chef.io/docs/scan-jobs/
Automate 1 documentation: https://docs.chef.io/automate_compliance_scanner.html

A2 documentation is a little confusing because it really talks about the API on the Automate side but you can access the scan job functionality in the UI as described above.