You won’t know if he’s lying to you, but if HE has any interest in rebuilding your relationship into something strong this is his opportunity to do so.
If you calmly explain that you’re feeling anxious about this trip, his reactions - whether guilty or not - will go some way to either reassuring you that he has no intention to cheat, or fuelling your fears. Some of that might be obvious (defensiveness, turning it around onto you, making your ‘insecurity’ an issue rather than his cheating etc) and some of it might be down to tuning in to your gut when he speaks about the trip.
Imagine you were him, what would you do, say and ensure to convince your wife she could trust you?
What would you do, say or ensure if you wanted to cover up the fact you were meeting someone else there?
I know some people are good liars and you may never know, but start the conversation and see what he says.
FWIW I’d be looking for an acknowledgement that he understands why you’ve asked and appreciates your humility in accepting that it’s an uncomfortable situation for you both having to talk about this, but that he knows he has to be open. I’d want (not too many!!) details about the place he’s staying, who’s going, whether he’ll be contactable etc.
When my XP went abroad for work I used to worry, as he’d always have tales about his colleagues cheating while they were away. I had no reason to suspect him btw but it’s always there as a possibility isn’t it. He was always open with the hotel name, who was there, he would FaceTime me every night and chat before bed, send me messages in the mornings etc so I always knew I was on his mind, even if it was just a brief hello. None of this would have been impossible if he was cheating of course, but the reassurance that he was thinking of me went a long way to making me feel happier about him being away - sometimes for weeks at a time - with a bunch of amoral a*holes and some beautiful younger colleagues.
You can only control your part in this, which is to open up about your worries, don’t play games turning up unannounced etc and just breathe.