Judging by pencil marks Stalin read with attention "On war" by Clausewitz, "History of military art" by Svechin, and "Strategy" by Leer. Yet it is not clear when he did that (probably after the war start).They have all of Stalin's books and I have seen a list of the titles somewhere, probably at the Hoover Library so probably at Rusarchives.
There were many thousands of volumes in the Stalin's library, some of them on military topics. Again, it is not clear which of them he actually read.