CORRECT TEXT
In which directory is the Linux kernel documentation be found?

Answer: /usr/src/linux/Documentation

Explanation:

See http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/usr.html
/usr/src/linux/Documentation Contains documentation that may be necessary in order to recompile a kernel. However, it also provides quite a lot of information about your Linux system in
general as well. For those who wish to seek further information on the contents of this directory
you may consult the /usr/src/linux/Documentation/00-INDEX file. Further, more detailed
documentation may be found in /usr/src/linux/Documentation/Docbook.