I'm not sure I follow... what is the spirit of truth? And how does one witness that something is truth?
Since nobody appears willing or able to answer your question, the Spirit of truth is not a what, but a who. And the who is the Holy Ghost, whose name is the LORD, the only begotten of the eternal God.
'Because I will publish the name of the LORD: .....'
'..... for all his ways are judgment: a God of truth and without iniquity, just and right is he.'
Deut 32:3-4
16 And I will pray the Father, and he shall give you another Comforter, that he may abide with you for ever;
17 Even the Spirit of truth; whom the world cannot receive, because it seeth him not, neither knoweth him: but ye know him; for he dwelleth with you, and shall be in you.
18 I will not leave you comfortless: I will come to you.
John 14:16-18