Here are craft book suggestions from the Facebook Group The Playwright Connection.
Dramatists Toolkit, The Craft of the Working Playwright by Jeffrey Sweet
The Art of Dramatic Writing by Lajos Egri
The Art and Craft of Playwriting by Jeffrey Hatcher
Dramatic Writers Companion by Will Dunne
Backwards and Forwards - A Technical Manual for Reading Plays by David Ball
Poetics by Aristotle
The Hidden Plot by Edward Bond
Theatre of the Oppressed by Augusto Boal
Brecht on Theatre by Bertolt Brecht
The Hero with a Thousand Faces by Joseph Campbell
How to Write Like Chekhov by Anton Chekhov
Lazzi by Mel Gordon
On Dramatic Method by Harley Granville-Barker
Obedience, Struggle & Revolt by David Hare
Three Uses of the Knife by David Mamet
Theatre by David Mamet (geared toward actors & directors)
The Theatre Essays of Arthur Miller by Arthur Miller
100 Essays I Don't Have Time to Write by Sarah Ruhl
The Ground on Which I Stand by August Wilson
The Crafty Art of Playmaking by Alan Ayckbourn
The Playwrights Guidebook by Stuart Spencer
Playwriting with a Purpose by Jacqueline Goldfinger (and her reading list of plays to look at for different topics/skills)
Playwriting: The Merciless Craft by Carols Wolf
Letters to a Young Playwright: Practical and Impractical Advice on the Art of Playwriting by Adam Szymkowicz
Playwriting Seminars 2.0 by Richard Toscan
How to Write a Play by Raymond Hull