Open a new Chrome window in Incognito mode from terminal
Use something like:

open -a "Google Chrome" --args --incognito "https://en.wikipedia.org/wiki/Main_Page"

Google Chrome accepts --incognito as a command-line option.  To pass that option to the application via open, specify it after the --args flag.

If Chrome isn't already open (since this was not specified whether the original questioner needed to launch it fresh or if it was already running), -n is also needed to start a fresh instance.

In general, man open is your friend.