Want to have a deep knowledge on a particular subject? Then take some time out of just reading about it and get active. Write a paper on it.
While I was tutoring logic in college, a technique I would sometimes use would be to have the student try to “teach” me how to do a particular problem. Why was this useful? It helped the student take a step by step approach to the problem. They were forced to try to see the most significant aspects and explain them.
See the Problem
Often, in order to understand a concept, we need to see how it will apply to a particular problem. Writing a paper that attempts to solve a problem will make sure that you are able to understand the idea. It will be a firing a pistol at a target. In order to hit the target you must know how to fire the gun.
Think of Plato’s Republic. Within it, he describes a society which has a philosopher king at the helm. In order to write to understand, try asking the question of whether or not a child trained from birth to be a philosopher king would really benefit a society.
The trick here is that in order to answer that question you have to have a clear understanding of why Plato thought it might be the case.
Counter Your Own View
To really test your mettle, have a section in the paper devoted to trying to destroy your own thesis. Take this part seriously. You want to be able to give the opposition its strongest ammunition and then shut it down. Doing so will show you have truly thought through the problem.
Keep It Narrow
Have the focus of the paper on a narrow subject. Having too broad of a subject will only allow the paper to skim the surface of the material. To really learn deeply about the subject pick a specific topic to deal with. You will find that to answer that specific question you will have to call upon knowledge about the whole subject. You will be forced to know it all.
Hopefully these points will allow you to write on a topic in such a way as to increase you knowledge of it in a deep way. You will know the ins and outs and be able to carry on a conversation with a person on the topic in a meaningful fashion.