In plain English
FAR 52.214-6, Explanation to Prospective Bidders, is a solicitation provision prescribed at FAR 14.201-6(c)(2), most recently dated Apr 1984. The complete official text is reproduced below, verbatim, from GSA's published FAR source files.
Its text contains no sentence requiring insertion into subcontracts; see the flowdown section below for what that does and does not mean.
Does it flow down to subcontracts?
No flowdown mandate found in the clause text
This is a solicitation provision — it applies to offerors when submitting an offer, not to contract performance, so subcontract flowdown is generally not the operative question for it.
Where it's prescribed
As prescribed in 14.201-6(c)(2), insert the following provision:
Prescribing reference: FAR 14.201-6(c)(2).
The official text, verbatim
As prescribed in 14.201-6(c)(2), insert the following provision:
Explanation to Prospective Bidders (Apr 1984)
Any prospective bidder desiring an explanation or interpretation of the solicitation, drawings, specifications, etc., must request it in writing soon enough to allow a reply to reach all prospective bidders before the submission of their bids. Oral explanations or instructions given before the award of a contract will not be binding. Any information given a prospective bidder concerning a solicitation will be furnished promptly to all other prospective bidders as an amendment to the solicitation, if that information is necessary in submitting bids or if the lack of it would be prejudicial to other prospective bidders.
(End of provision)