Which means of knowledge (pramana) involves deriving knowledge from linguistic utterances of reliable persons?

Knowledge gained from the linguistic utterances of a trustworthy person is verbal testimony.

Here the source is the meaningful statement of a reliable authority, understood through words.

It differs from perception, inference and postulation, which do not rest on another's spoken words.

The classical means that yields valid knowledge from reliable speech is shabda.

So the pramana in question is verbal testimony, shabda.