In plain English
FAR 52.252-2, Clauses Incorporated by Reference, is a contract clause prescribed at FAR 52.107(b), most recently dated Feb 1998. 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
We scanned the full clause text and found no sentence directing the contractor to insert this clause into subcontracts. That is a statement about the text, not legal advice: a prime contractor may still flow terms down contractually, an agency supplement (DFARS, VAAR, …) may add requirements, and clauses listed below (if any) may order this clause into subcontracts from the outside.
Where it's prescribed
As prescribed in 52.107(b), insert the following clause:
Prescribing reference: FAR 52.107(b).
The official text, verbatim
As prescribed in 52.107(b), insert the following clause:
Clauses Incorporated By Reference (Feb 1998)
This contract incorporates one or more clauses by reference, with the same force and effect as if they were given in full text. Upon request, the Contracting Officer will make their full text available. Also, the full text of a clause may be accessed electronically at this/these address(es):
_____________________________________________ _____________________________________________ _____________________________________________ [Insert one or more Internet addresses]
(End of clause)