Credential-less Discovery is a feature of ServiceNow Discovery that allows the instance to identify configuration items (CIs) without using credentials. Credential-less Discovery uses Network Mapper (Nmap), a free and open-source network scanner, to collect information about the CIs by sending packets and analyzing the responses. Nmap must be installed on the MID Server that runs Credential-less Discovery. Credential-less Discovery can be used as a fallbackoption when credential-based probes fail, or as a primary option for scanning certain types of devices, such as network devices, printers, or IoT devices12.
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Credential-less Discovery with Nmap - Product Documentation: San Diego - Now Support Portal Credential-less host Discovery - ServiceNow - Now Support

The Debug Identification Section in Debug Mode allows you to specify the identification attributes of a CI that you want to debug. These attributes are used to find the CI in the CMDB and run the pattern on it. The identification attributes vary depending on the CI class, but for infrastructure patterns, the common ones are IP and Host Name. These attributes are also used by the horizontal discovery to identify CIs. AWS Endpoint and PID are not valid identification attributes for infrastructure patterns.
1: The explanation is based on the following sources:
Activate pattern Debug mode: This document explains how to activate the Debug mode and use the Debug Identification Section to debug a pattern.
ServiceNow Exam CIS-Discovery Topic 6 Question 9 Discussion: This discussion provides a similar question and answer about the Debug Identification Section in Debug Mode.