Do some research on who will be attending the trade show, who are the keynote speakers and what topics they will be speaking about. Usually, when you register for the event, the website that markets it will breakdown each day in a schedule as well as who is speaking and the topic being discussed.
There are a couple options that I use to conduct an interview.
First, always ask up front if you can record the audio and or video of the conversation.
If A-OK then I use my smartphone for everything. If it's just the audio, then I have an app installed on my phone that records speeches or lectures. If I'm recording video the I usually ask someone to hold the phone and record it or I also have a selfie stick.