The correct answer is D. Building a search terms report. Relativity's Search Terms Report documentation requires you to define report information including a Searchable Set, which is a saved search containing the documents to be evaluated by the STR. Relativity's guidance for using STRs also states that you should define a saved search that returns the required document population for the searchable set. That makes a saved search a required component of building a search terms report.
The other options do not inherently require a saved search. A keyword search can be run directly in the search panel. A dashboard can be created without requiring a saved search as its core prerequisite. A persistent highlight set is commonly used with STR output, but the question asks which action itself requires a saved search, and the STR workflow is the one explicitly documented to require one. Therefore, the correct answer is Building a search terms report.