Actually this is the default functionality of woocommerce. Whenever you use three attributes in your product and generate variations for that product and then add that product to cart. It will display the attribute names before the variations as in the screenshot: https://jmp.sh/tKdIMvA

–> No, I use only two attributes, not three, it still show. Look at this screenshot https://www.dropbox.com/s/jhkofsqp79ivz17/sc8.jpg?dl=0

But whenever you used one or two attributes which are less than three then the attribute names will not shown along with the variations in the cart and they just separated as in the below screenshot: https://jmp.sh/MrMxOKV

–> No, I use only two but it shows. Look at this screenshot https://www.dropbox.com/s/jhkofsqp79ivz17/sc8.jpg?dl=0