Location of /etc/fstab in El Capitan I want to activate the NTFS support.
But I can't find the /etc/fstab on my mac.
osx 10.11.5 El Capitan
/etc/fstab doesn't exist by default, only if anything has previously needed it. fstab itself is merely a text file. If nothing has previously needed one, you can make it yourself.

The standard header appears to be a comment with vague instructions as to how the syntax works...

# fstab
#
# Identifier  mount point  fs type  options1
#


below that is your mount or ignore instruction, e.g. 

UUID=C126C736-1585-3D12-9CF1-F95EFF0CF744 none hfs rw,noauto  


or  

LABEL=[drivename] none ntfs rw,auto,nobrowse


There is far more information on fstab at https://developer.apple.com/legacy/library/documentation/Darwin/Reference/ManPages/man5/fstab.5.html than I could possibly précis here, or type man fstab in Terminal.