If (and I don’t know for sure) there is no dedicated headphone jack, you can use the A/V jack for this.
First (just to try it) plug in a set of phones directly to the A/V jack and listen to see if it works that way.
(My Panasonic home video camcorders allow headphone monitoring from the A/V jack by way of a menu setting.)
If the audio from the headphone has a loud buzz in the left channel, then you are hearing the VIDEO coming thru the “tip” of the headphone plug.
If that’s the case, you will need to utilize the A/V CABLE connected to the camcorder’s A/V jack… and connect the headphones to the Red and White RCA leads via an adapter (to allow the RCA’s to “feed into” a jack that the headphones will fit.)
A sensitive set of headphones will give you louder audio.
If the level is too low, you may need to use a headphone amplifier to boost the audio level,
Google “Boostaroo” for more info on that.
I’m too polite to ask you why you bought TEN cameras without fully checking ONE before the purchase, 😉