I found it on the internet as part of an AP history DBQ. I have taught AP European History, so hopefully I will be of some help. When you interpret cartoons, you need to list (mentally or on paper) just what you see. You also need to have some background knowledge about what is going on. The main thing you are doing is to tell what the artist is trying to tell the public about that situation.
You already know it has something to do with Queen Victoria, Chamberlain, and South Africa. What is QV doing? She is painting a picture on the wall, and the picture is a map. Chamberlain leans over to advise her how to paint South Africa. Who is Chamberlain? He was Secretary of State for the Colonies. We see part of a person holding the paint pot. Who is that person? From the sword and uniform, it is a soldier, and the paint is blood.
The artist is saying that Victoria is like a fat old lady with a lady's hobby. She is not in control of her empire. Chamberlain is directing what she does and is a bad influence. He will force her to involve Britain in a bloody war in South Africa.