The correct syntax to find events associated with a tag in Splunk is tag=1. So, the correct answer is D. tag=. This syntax allows you to annotate specified fields in your search results with tags1.

In Splunk, tags are a type of knowledge object that you can use to add meaningful aliases to field values in your data1. For example, if you have a field called status_code in your data, you might have different status codes like 200, 404, 500, etc. You can create tags for these status codes like success for 200, not_found for 404, and server_error for 500. Then, you can use the tag command in your searches to find events associated with these tags1.

Here is an example of how you can use the tag command in a search:

index=main sourcetype=access_combined | tag status_code

In this search, the tag command annotates the status_code field in the search results with the corresponding tags. If you have tagged the status code 200 with success, the status code 404 with not_found, and the status code 500 with server_error, the search results will include these tags1.

You can also use the tag command with a specific tag value to find events associated with that tag. For example, the following search finds all events where the status code is tagged with success:

index=main sourcetype=access_combined | tag status_code | search tag::status_code=success

In this search, the tag command annotates the status_code field with the corresponding tags, and the search command filters the results to include only events where the status_code field is tagged with success1.