What exercise do I need to avoid if I am having knee pain in one leg.
Can someone guide how to maximise muscle build up without putting too much effort on knee.
Hey and welcome to the forum 
firstly, freeletics is mostly for healthy people and I think your knee problems may be too restricting for the coach. You should ask your doctor about which movements you shouldn’t do and exclude them, but you can only exclude 10 exercises… Maybe the “train quietly” option could be good for you too.