What would a painter do in ancient europe?

I am not sure what type of painter you mean. If you mean a house type painter there wasn't any. House painting is a modern job and there wasn't any paints made in the middle ages. Actually, all the way into the 1930's and 1940's to paint a house was very expensive and very few people had a house that was painted. If you mean an artist he would have been an artist for the church and painting religious subjects. The art of the time was all religious and egg tempera was used as paint on wood planks. Some still exists, but historical information in art mainly comes from books made by the monks and on tapestry.