There aren't many books that describe deep value investing and net-net investing in detail. This is perhaps because the strategy is increasingly forgotten in favor of buy-and-hold long-term competitive advantage value investing advocated by Warren Buffett et al. Deep value investing was of course described in Security Analysis by Graham and Dodd within a one or two chapters, but that book is very old and deals with much more than just stocks. Here are some newer books I found that focus on contemporary deep value investing:
Deep Value Investing by Jeroen Bos.
Remember to get hold of the appendix as well (freely available online from the publisher). It contains all the details, numbers, and financial statements discussed in the book. It is also longer than the book.
Benjamin Graham's Net-Net Stock Strategy by Evan Bleker.
Deep Value by Tobias E. Carlisle.
I haven't finished reading all three yet, but I hope you will. Happy reading and good luck!