This will also depend on the role you are interviewing for, focusing on UX design and UX research here.
For a UX design position, you can expect to discuss your portfolio in detail and/or do a design case study. In both cases, be prepared to explain your thought-process as you go along. It’s more important to show that you can critically think about a problem and that you know the steps/tools to tackle it, than it is to properly solve it during the interview. UX design can mean a lot of different things, make sure you are clear on what your skillset is within UX (research, wireframing, architecture, prototyping, graphics…) and what you will bring to the table. Some companies know they need a UX designer but aren’t clear about what they need the designer for, you may need to educate them about why they need you.
For a UX research position, you can expect to solve a case study by mapping out a research plan and/or presenting your past research projects. This type of position tends to be more specific than UX design and more commonly found in larger and more established companies. Because of that, you can be expected to conduct a usability audit of their product – so make sure you come prepared with your own research of the company you are interviewing with!
I highly recommend this talk by Jared Spool (https://www.youtube.com/watch?v=PwDJqBW2gs4) and following him on Twitter (https://twitter.com/jmspool)