Well, you can only really show it if they ask you the common question "Why do you want to work in <blah>?"
In which case, you can frame a short answer that answers specifically that and integrates current knowledge. E.g. <blah> is leading cutting edge <blahness>, such as with <blah> <blahrifically>
Otherwise, if you have case studies, etc, you can demonstrate business knowledge through the exercise itself. Probably wouldn't hurt to look up quick financials if relevant (share price, etc) and recent press releases.
Thanks guys! Yeah, you right, you have to answer the questions they ask. But I also was wondering what areas you would look into because I found few recent deals, their awards, expertise in practice areas, offices etc.
I am not sure if it is enough and if I should know the ins and outs of the deals I will mention because usually detail is scarce on their websites.
One firm asked their PEP (Equity per partner) and I was like 'what?' xD. But now I find all that info too, even their managing partner name.