Breitbart and Daily Stormer both claim they're the platform of the alt-right, both with some legitimacy. Read Andrew Anglin, Richard Spencer, and the collective shitheads at Breitbart. Hunt down stuff Stephen Miller wrote. Read what you can of Bannon's. Those are the driving forces behind Trump's
"economic nationalism".
Most of their philosophy rejects expertise and academia, so you're not likely to find any scholar specifically writing about Trump's political philosophies, as distinct from traditional GOP philosophies.
It's youtube videos, blogs, and articles, mostly.