1. Knowledge of each and every concepts of that topic.
2. Proper understanding with real life scenarios for each of them.
3. We are not supposed to by heart anything.
Organisational Structure topic can’t be the exception for the above rules.
PMBOK has given different diagrams for different types of organizational structures. You are supposed to understand each of them and then start comparing them with diagrams of other types. This comparative study can help you to understand even minor differences between different organization structures.
For each diagram, you are supposed to find the best suitable example. These examples can help you to relate between theory and practical.
Next step is Table 2-1 from page no 47 of PMBOK Guide 6th edition. This table will tell you how responsibilities are shared between Functional Managers and Project Managers; and how those responsibilities are either increasing or decreasing with respect to the change in organization type.
This table is the key for the topic.