You will hear the left audio from mono 1 and the right audio from mono 2, but if you are plugging a stereo headset into either one of them, you will always hear the audio through the same side of the headset. I can’t remember exactly, but I think that will always be the left side. That is because a mono plug is essentially the left side of a stereo plug. Mono has only one side.
If you want to hear mono 1 through the left side and mono 2 through the right side, that is actually stereo. You don’t want to use the mono adapter in that case. What you want to do is use a balance/pan control set all the way left to hear the left side of the audio in your left ear and silence in the right, and then set the balance/pan all the way right to hear the right side of the audio in your right ear and silence in the left.