In order for a search collection to create audit log entries, the audit log must be enabled in the configuration for that search collection. If you want all new search collections to create audit log entries, you should enable the audit log in any search collection that you use as a template so that any new search collections that are based on that collection will inherit those settings.
The entries associated with the audit log are located in the Configuration > Crawling screen for that search collection:
You can also add support for the audit log to an existing collection by adding XML to that collection, as described in Enabling Crawl Options in the Watson Explorer Engine Administration Tool. To manually add support for the audit log, you will have to add the following crawl-option entries in addition to those discussed in Configuring Light Crawler Mode in the Watson Explorer Engine Administration Tool:
<crawl-option name="audit-log">all</crawl-option> <crawl-option name="audit-log-detail">unsuccessful</crawl-option> <crawl-option name="audit-log-when">finished-or-replicated</crawl-option>
These values will enable the default values for index-atomic operations and the audit log, and will cause separate audit log entries with the replicated="replicated" attribute to be added to the audit log when replication of that entry is completed. This is just an example - you can also specify any other, valid values for these options - see Logging and Examining Enqueue/Delete Status for detailed information about other possible values for each option.