And where is it located?

Big sets like that generally don’t have headphone jacks. See the ref below for the specs on this one.

The way I get around that with my 46-inch set is to use the headphone jack on my surround sound amplifier. I just turn the audio on the TV all the way down, then plug into the headphone jack on the amplifier. Works great, plus I can use the remote for the amp to adjust audio level in the headphones. This is a neat arrangement when I’m watching some noisy action movie that the wife would fine annoying.

With a big set, you’ll want a long extender cable for the headphones, or dedicated wiring between the amp and your viewing position.