Why can't I find MAKEDEV in the /dev folder?

Your book was correct when it was written, but it is now obsolete. MAKEDEV used to be a script in /dev, potentially supplemented by a local MAKEDEV.local written by the system administrator; nowadays, if it exists, it’s more likely to live in /sbin.

Many current Linux systems don’t have a MAKEDEV at all, they rely on the kernel and udev to populate device nodes as necessary.

See Why is the name of the MAKEDEV script spelled in all caps? for more on the history of MAKEDEV.

As per @StephenKitt's comment, the book must be outdated; see Why is the name of the MAKEDEV script spelled in all caps? .

Actually MAKEDEV is in /sbin/. From the man page:

Name

MAKEDEV - create devices

Synopsis

/sbin/MAKEDEV -V
/sbin/MAKEDEV [ -d directory ] [ -D directory ] [ -c configdir ] [ -m maxdevices ] [-a] [-n] [-v] [-i] [-M] [-S] [-u] [-x] " device ..."

Description

MAKEDEV is a program that will create the devices in /dev used to interface
with drivers in the kernel.

Note that programs giving the error ''ENOENT: No such file or directory''
normally means that the device file is missing, whereas ''ENODEV: No such
device'' normally means the kernel does not have the driver configured or loaded.