"To master the topic" means to have a deep understanding and knowledge about a particular subject. It involves being able to confidently explain and apply concepts related to the topic. Full definition
Several of the students, she said, still hadn't mastered the topic. (edweek.org)
The lesson shows by way of examples what the pupils need to do in order to master the topic so that they can confidently answer any relevant questions on this topic. (tes.com)
This resource is prepared with the intention of helping the higher GCSE pupils and the AS level pupils to understand the topic of the equation of a circle and master the topic with ease so that they can answer all related the questions without difficulty. (tes.com)