Can congress issue a finding of contempt of congress, or does a federal judge have to do that?
Well, hell, who knows; they're making it up as they go along!
Maybe they can.
U.S. Congress generally brings this action for refusing to testify before a Congressional committee, or failing to provide a committee with requested documents. There have also been contempt cases based on bribing a Senator or Representative.
But since the Senate adjourned, who the heck knows.