I haven't been able to get it to work.
Last week, while I had my G751JY (i7 4720HX / GTX 980M) disassembled to replace a bad DC jack, I swapped in the entire top assembly from a touch-screen-equipped G751JL (i7 4720HX / GTX 965M) that has a bad motherboard.
The JL model uses the same BIOS and driver software for both the touch- and non-touch JL variants. Since touch is ubiquitous on notebooks these days, I had assumed that Asus would have included support for it in the software and firmware for all later models in the G751 family (especially for ones, like my JY, that shipped with Win 10 installed), regardless of whether they planned to release a touch-screen configuration of the model.
I was apparently wrong. I have found no way to get the system to recognise the presence of the touch screen capability. (no HID-touch Screen entry shows up in dev mgr and Tablet Settings says it's a non-touch display.)
There's nothing in the BIOS to turn it on (nor was there on the JL, so that was no surprise), and I couldn't find any driver (neither for Win 10 nor 8.1) from Asus that looks to be related to it.
Is it maybe handled by the graphics card? Might updating the nVidia drivers for the 980M help? (Or...gasp. . .the VBIOS firmware) Or is it perhaps that touch is only supported on the GTX 965M? (However, I found nothing to suggest that that might be the case.)