As far as I know, for my 2 years experience at Automation testing using Selenium, I think they would probably expect you to understand the tool as a whole and it’s underlying programming language being used such as Java, Python, C# etc.
Below are some of the important Selenium Interview Questions that can be asked from you:-
Xpath - Relative and Absolute.
What is the different type of ‘selectors’ used?
Gave a scenario and enquired on how to navigate to the exact location using Xpath even if the ‘HTML tag’ being used is dynamic in nature ( Whenever, we open a page, the ‘HTML tag’ for that field, will change every time)
Capturing screenshot and reports.
What are TestNG and JUnit?
Usage of any third party tools and integrating it with Selenium such as Auto-IT, Sikuli, Jenkins, ANT etc.
Usage of any repository such as GitHub etc.
Different wait functions such as Implicit Wait, Explicit Wait, Fluent Wait, WebDriver wait
Usage of any Automation framework or if given a chance, ‘Have I built and how’
Capturing all the values in a dropdown/table and displaying it as output - Usage of Java collections.
If you are interested in making your career in the testing field then you must take up the following Selenium Training Course. If you are interested in reading the stuff then you must read the following Selenium Tutorial. Here is a video tutorial which you can watch to learn all the basics concepts of selenium. .