Sony FX 6 Quick Start Manual page 37

Audio: Headphone Jack
The headphone jack is placed on the side of the
camera. The output level for the headphone jack is
in the menu/ audio/ audio output/ volume. You can
also select in that menu whether this is a stereo or
mono output.
The camera kit does not come with headphones.
I recommend reserving the Sennheiser HD 280 Pro
enclosed headphones from the EV Depot.