In plain English
FAR 52.216-28, Multiple Awards for Advisory and Assistance Services, is a solicitation provision prescribed at FAR 16.506(g), most recently dated Oct 1995. 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 16.506(g), insert the following provision:
Prescribing reference: FAR 16.506(g).
The official text, verbatim
As prescribed in 16.506(g), insert the following provision:
Multiple Awards for Advisory and Assistance Services (Oct 1995)
The Government intends to award multiple contracts for the same or similar advisory and assistance services to two or more sources under this solicitation unless the Government determines, after evaluation of offers, that only one offeror is capable of providing the services at the level of quality required.
(End of provision)