Just search the State Dept. server for anything sent OR received to OR from Clinton’s email. How hard is that?
The problem is any emails sent to or from Hillary's personal server to another private email address never went through the State Dept. There's no way to know about those, unless the NSA happened to be watching those private emails.
Be certain the FBI has done that, maybe weeks ago.
Also probably has seized any/all commercial email accounts of everyone they believe involved.
And by now they are following up on every address in/out, reviewing content and following up on all the traffic in/out of those 3rd parties.
They MUST determine the extent of the leak of Top Secret information...not just the email, the information.
This may take months but they WILL know.