I think it is a bit naive to believe that the FBI agents after seizing the computer haven't looked at them. I also doubt that they would have immediately realised that they would even need a separate warrant for those emails. Thirdly we know that FBI agents have already questioned Huma about some emails.
Obviously once they realised they need a separate warrant for the emails Comey is saying he doesn't know....but it's naive to think he doesn't know what's in them
It doesn't matter what's in them (or not). What Comey has done is to allow Trump to go around the country blathering that she's guilty and should be locked up, based on an FBI statement that they found emails not sent by HRC to a computer not HRC's, that may or may not be significant to a case which was never closed (there is no "new investigation").
Politically, the right thing for Dems to do would be to get the media OFF this fixation. If they don't have another Trump bombshell to drop, they should just be repeating "Trump sexual offender", "Trump fraud" and "Trump bribery" ad nauseum. And if the media doesn't take notice, they would need to simply Trump it up a little by saying he's guilty of all those things and they
"want him locked up NOW!"