for the X its on the gantry upright, using a screw in a t slot as the pickup point. so, 1 sensor, and 1 (home) or 2 (each end hard limit) pickups.
for the y and z its done a bit odd. they y (gantry cross) theres is meant to be 1 or 2 sensors on the back plate that pick up the aluminium moving y saddle/ ball nut mount. one sensor for each end. this works. realistically, you just need one sensor for home, and then use soft limits.
the z is the same as the y, but its got one switch meant to pick up the z saddle at the top (home).