What M.2 drive to get for this laptop?

Hi, so i am IT and its really awkward for me but i have a hard time understanding how this drive connectivity works.

Here is a laptop: ASUS ROG GL552VW - I have been asked to install an M.2 SSD in it but i am really confused and i have a few questions.

Question 1: How can i find out if it uses the SATA or the PCI controller? And if uses one over the other is it compatible with both?

Question 2: How to pick the right size? All it says: - 256GB SSD (M.2 2280) on the website but it does not say if its a B or M connector at all. ( I assume the 22m is the width and the 80mm is the length)

I am thinking about getting this WD 120GB Green M.2 SATA M.2 2280 drive. According to the site its Sata controlled. Is it going to be compatible? ( it looks like it supports B and M)

Thank you for your answers!