I seem to be missing one black book. So what are all the locations of the black books? How many are there in total?
There are seven Black Books in total. The wiki page gives these locations:
Epistolary Acumen - Found in Nchardak during the quest "The Path of Knowledge".
Filament and Filigree - Found in Kolbjorn Barrow during the quest "Unearthed".
The Hidden Twilight - Found in Tel Mithryn, next to the Staff Enchanter.
The Sallow Regent - Found in White Ridge Sanctum, you will have to go through the White Ridge Barrow first.
The Winds of Change - Found in Bloodskal Barrow, during the quest "The Final Descent".
Untold Legends - Found in Benkongerike, after the word wall.
Waking Dreams - Found in the Temple of Miraak during the main questline.
You can also get the Black Book locations from Neloth in the quest Lost Knowledge - this is repeatable in the same way you can ask the Grey Beards for word wall locations. Doing it this way nets a handy 1000 Septims for each completion.