The hint is implemented unusually. To see which knuckles are available for the move, you need to click on the HINT button at the top of the screen in the middle. And then all possible pairs will be displayed for you. But only the names of the knuckles will be displayed which can be removed. You have to look for them by your own.
To play in this kind of mahjong in the whole screen is much more interesting and convenient, because you can see all the charms of a customizable background, color and type of chips, not allowing your eyes to get tired of many small details.