Final answer:
In Splunk's configuration files, the source type can be omitted in indexes.conf, which deals with index settings and not data source types.
Step-by-step explanation:
The .conf file in which you can omit the source type is indexes.conf. In Splunk's configuration files, the source type can be omitted in indexes.conf, which deals with index settings and not data source types. In the context of Splunk, which is what these configuration files relate to, indexes.conf is used to configure index settings, and it is not concerned with the source type of the data.
The sourcetype is typically defined in inputs.conf, where you specify parameters for data input and ingestion, while props.conf and transforms.conf are used to specify how the data is parsed and formatted. Therefore, only in indexes.conf the sourcetype specification can be omitted without affecting the indexing process.