The educational industry has evolved with the development of computer technology. The online education system (OES) provides a more effective and efficient educational strategy for students benefiting from computer science technologies. There is a need for a mapping of knowledge definition from the traditional education system to the data gathered from the non-traditional OES. This would make the measurement of knowledge possible for OES. The study aims to (a) find an appropriate knowledge definition through a literature review process, and (b) based on the definition measure students’ knowledge in OES, such as Hypocampus, by using machine learning techniques. Experiments were conducted using a well-known Bayesian KnowledgeTracing (BKT) model. The evaluation was performed on 3300 students studying medicine in France using Hypocampus OES. As a result, the student’s knowledge was measured in skills, performance, and achievement per subject with 81% average accuracy. The obtained results suggest the potential of the presented approach for measuring students’ knowledge in OES.