We introduce DZEMUj, a system for mining in e-learning data, namely in electronic tests and DIA, DZEMUj Intelligent Assistant. DZEMUj farther extends capabilities of the elearning module of the Information system of Masaryk University and offers a set of tools for data analysis. DZEMUj enables to find the most difficult and/or the easiest test queries, to discover associations between answers and also between behaviour of students. We shortly describe data preparation, namely data transformation and data pre-processing. Then we focus on knowledge discovery and knowledge visualization - a scatter plot, RadViz and frequent patterns. DZEMUj has been testing on data from the e-learning module of Information System of Masaryk University since January 2008. DZEMUj is quite efficient. For 507 students, 80 different questions, 10 questions in a student test, the analysis finished in less then 1 minute. DZEMUj is implemented in python, java and R. We conclude this part with evaluation of DZEMUj. Then DIA, an intelligent assistant for DZEMUj is described.