File Extension OBK File Format UbiSoft ChessMaster opening book file OBK stands for UbiSoft ChessMaster opening book file. This was last updated in March 2012 By Margaret Rouse Browse File Extensions Alphabetically: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # Ask a Question. Find an Answer. Ask your peers a question about this file extension. Ask a Question IoT, NFC and 'The Internet of Mysterious Things' Opening MDB file with Apple iBook What is CRDOWNLOAD file and how to open?