On the previous release of CA Service Desk, it is done by adding the custom field to a *.mod file, such as cr_site.mod file.
On CA Service Desk 12.9+, it is set through Web Screen Painter.
This document explains how to generate an Activity Log when the custom field is updated on r12.9 and later
Release: 12.9 and higher
Component: CA Service Desk Manager
In this example, the Activity Log "Field Update" will be logged when the custom field "zresolved" is update.
OBJECT cr {
ATTRIBUTES Call_Req {
zresolved INTEGER { UI_INFO "AUDITLOG";};
};
};