Hello,
SONAR is the real-time protection that detects potentially malicious applications when they run on your computers. SONAR uses heuristics as well as reputation data to detect emerging and unknown threats. SONAR provides "zero-day" protection because it detects threats before traditional virus and spyware detection definitions have been created to address the threats.
Sonar is an Integral Part of SEP 12.1 and could not be removed. However, you can disable the protection from SEPM.
Check this Screenshot:
Check this Thread with similar query -
https://www.symantec.com/connect/forums/how-disable-firewall-and-sonar-status
Hope that answers!!