Since the User Interface (UI) is one of the most critical parts of any application, you can expect a lot of questions about this topic. As a developer, you should be able to address these based on your education and experience. Be sure you can discuss the business benefits of a good UI design since this is important to companies developing commercial applications.
"The User Interface, or UI, is probably the most important feature of a well-designed application. No matter how good an application functions, a bad UI will make it difficult to use and frustrate the users. The key to developing a good UI is to take steps to understand how users will interact with the application and what platforms they will use it on. Making the UI responsive so it will have the same look and feel across a variety of platforms is also important. Finally, the UI should be tested with actual users to confirm that your assumptions are correct and to address any issues they identify before the application is released."
"When I begin a development project, I start with the User Interface, also known as the UI. Since this is likely the only part of the application the users will see and interact with, it is important that it is done correctly. I meet with prospective users and discuss the purpose, functions, and features of the proposed application. I then solicit their feedback about how they would like to interact with the application and what are the features of the UI they would like and not like, such as buttons, menus, appearance, and other items. Once I have built the UI and before I release the app for use, I meet with users to have them test the UI and provide me with their feedback, so I can fix any issues they identify."