Even if Trump didn't know (unlikely), his Chief of Staff most assuredly did:
A former American official said the national security adviser, Robert C. O’Brien, and the president’s chief of staff, Mark Meadows, would have been involved in any decision to brief Mr. Trump on Russia’s activities, as would have the intelligence analyst who briefs the president. The director of the C.I.A., Gina Haspel, might have also weighed in, the former official said.
Ms. McEnany cited those three senior officials in her statement saying the president had not been briefed.
The most likely scenario is that Trump was (verbally) briefed on the issue, as well as having it included in his daily intelligence packets (which he probably didn't read). But whether Trump knew or not, his current position of, "I don't believe it, it's not credible," is a direct assault on the integrity of our intelligence community and Special Operations who put themselves in harm's way to uncover this deadly plot: