How can the government compel private citizens to answer questions for the Russian interrogators?
It can't.
But it can ruffle the feathers of the Deep State. (Let Trump just hint at negotiating an extradition treaty with Russia, and watch them go completely ape****!)
Read the Treaty:
https://www.state.gov/documents/organization/123676.pdf
It says that Russia can request that the US issue a subpoena to any US citizen and require them to answer questions.
Of course, any US citizen can also refuse to answer (5th Amendment).
Conversely, the US government can request that Russia issue a subpoena to the GRU officers and require them to answer questions.
An interesting section in the treaty is for extraditing to answer questions, but to allow them to return to their home country within 7 days of answering questions.
A treaty is a real thing - read it :)
How can the US Government indite foreign nations on the basis of “secret” evidence?
Sauce for the goose. DOJ/Muller opened this clown show with their phony Russian incitements and now the Russians are responding in kind
So, of course, all the usual suspects are screaming in hysterics that the legal standard they want to apply are being applied to them