Can you please advise what cable is required for the LRT 2.5 timer for the Nikon Z6?

It's the default Nikon Cable, which is also used for the majority of all Nikon DSLR, like D750, D6x0, D7x00, D5x00 etc.
One side 3.5mm TRS (3 contacts) and on the other side the Nikon plug.
Couldn't you find it via the Amazon links provided on https://lrtimelapse.com/lrtpt/camera-release-cables/ ?

I own a Z6 and purchased this cable. It works nicely, The coiled cable provides stretch. I often do not need the stretch and wrap the cable under my lens, to get it out of the way so I don't hit it with my hands The cable info/link was provided by Gunther.

https://www.amazon.com/dp/B01MR48UZZ/ref...UTF8&psc=1