Here he is being interviewed by his son, DJTjr, and it's very interesting, listen to exactly what he says, his body language, hmmmmmmm? Sounds to me like he knows something, but was told not to tell, and knowing Trump, he's having a tough time keeping it to himself. Remember, Trump recently said, "I never kid". https://www.facebook.com/watch/?v=264730511616164
He has also said before that he doesn't believe in the existence of aliens. So, he probably doesn't know about that.
The three that know are Cheney, Rumsfeld, and Bush sr. Those three were in charge of every aspect of UFO intelligence throughout their careers and they compiled all the information and locked it away somewhere so even if a president wanted to know what it is, he wouldn't be able to. Wherever this information in or who's actually in charge of it is all buried deep in government paperwork and is an impossible trail to follow without the right connections. There's a Youtube video of Cheney being asked about UFO's and this information and it's extremely interesting to see him fumble with the question because he wasn't expecting it.