Can I ask questions to a witness?

Yes.

 

You have the constitutional right to confront your accusers.

 

That means you have a constitutional right to compel witnesses to appear in court.

 

You can compel the government to tell you who the accusers are; and require they come to court to make the accusations in front of you and the jury.

 

There is no such thing as trial by affidavit, sworn statements, or any evidence which cannot be subject to cross-examination and challenge.