I know I am a numpty, but could someone please tell me exactly where I find a command line so I can type in which mogrify

the only vague commands I can do in cpanel are cron jobs
Its not obvious anywhere and even google does not help.
I'm getting a thumbnail error and I know that the Image Magick path is
/usr/bin
or
/usr/local/bin
so do I just change
"/usr/bin/X11/mogrify" to something else?