The name knapper occurs in a number of northern european countries but if your family originated in England then there are two possible origins for the name. The first is toponymical ie named after a geographical feature, in this case a "knap" meaning a hill and means a hill dweller. Thisorigin most often quoted when I have reasearched the name, probably as the single source is being quoted. The other origin and in my opinion the more compelling is from the skill of flint knapping (shaping flints) as the people carring out this activity were and are known as knappers. This name occurs quite often in the east anglia region of england.