I know it’s hard for non-law students because you have to demonstrate an interest in a world that you haven’t yet studied. Your interview won’t require legal knowledge so don’t worry about that; interviewers know you’ve still got the GDL and LPC to do.
Instead, they’re trying to identify whether you have the potential, so try to understand what a commercial solicitor does and think deeply about why you’re interested in it.
Most law students won’t have an understanding of finance through their degree but yes, especially with the top corporate firms, you should be able to discuss the above on a very basic level. A lot of students struggle here because they pick out a complex story from the FT and then suffer when asked very simple questions. And I get it – it’s really hard to know where to even start with this as there’s so much to cover, I was in the exact same position when I first started.