It's impossible to say, without a direct clarification from the White House, which particular classified documents the President has in mind.
Saying that there were multiple calls from some of the congressional Republicans on the President to declassify and release the documents related to the Carter Page investigation and the Steele dossier.
Most recently, on Thursday, September 6, 2018 the group of House Republicans held a press conference to call on President Trump to declassify some of these documents.
Here's the relevant excerpt from the opening statement by Representative Lee Zeldin (NY-1):
I'm joined here today by several of my colleagues, including congressmen Meadows, Jordan, Gates, and others to call on the President of the United States Donald Trump to declassify and release important information for the American public:
There are three parts to our request:
One. We're calling for a declassification and release of the Carter Page FISA applications. While we strongly favor of releasing the entirety of the FISA applications except for the necessary reduction of any sources and methods that must truly remain classified we most specifically want to ensure that the President declassifies and releases 20 pages in particular of the last FISA renewal. This includes pages 10 to 12 and 17 to 34 along with the associated footnotes. We're confident that the FISA applications will prove that the highest levels of the DOJ and FBI failed to provide the FISA court with critically important information when they requested a warrant to spy on Carter Page and others.
Part two of our request is that we're calling on the President to declassify and release all twelve of the Bruce Ohr 302s. We're confident that these 302s contain critically important information that should have been provided to the FISA court but wasn't.
Part three. We're also for the declassification and release of the documents provided to the Gang of Eight that contain exculpatory evidence regarding Carter Page and others. We're confident that these documents also contain critically important information that should have been provided to the FISA court, but wasn't.
Later in the conference, representative Mark Meadows (NC-11) said that he already discussed the need for transparency with the President.
So here we have at least one package of documents the President might be referring to.