[generally]

I thought he might be looking at one of the guests above and behind him. I think that is approximately where Melania was sitting.

Anyone else have ideas on this?

It was a very distinct nod. Maybe just at Melania or one of the guests, but maybe something else.

[stylin19a]

Details from last year.

https://www.businessinsider.com/here-are-hidden-state-of-the-union-details-you-might-miss-on-tv-2019-2#aisle-hogs-will-park-themselves-up-to-six-hours-before-the-address-3

The Capitol press corps sit directly above and behind the president.