cocaine cravings

It would be a personal matter for him. Such cravings vary from person to person. So play it however you like.

I imagine he'd have pretty similar responses to any addict faced with the temptation of returning to their addiction.

I doubt too many people on here want to admit to being former (or current) cocaine users, which makes it a little difficult to answer your question.

He's probably going to have a hard time playing it cool. He'll be prone to sweating, maybe a little jumpier than he'd like to be. The dealer could wonder if he's looking for a fix, and offer to set him up. If he turns it down, the dealer could become suspicious, wondering what's wrong with him.

Whether he goes for the fix or not depends on what you want to happen next.

I was a smoker for a while. I found cravings for cigarettes to be similar to how I felt when I was (really) hungry or thirsty. Not really a physical sensation so much as a compulsive thought process.

Mostly your brain takes over and starts flooding you with ideas about how awesome it would be to go and get a bar of chocolate. Damn, that chocolate would taste delicious, it's the only thing that could satisfy you right now, a nice big chunk, maybe it would melt a little and...
It's the kind of thing that can sneak up on you.
Oh and when I'm really hungry I don't just think about eating a single square of chocolate. In my mind, I'm swimming in a chocolate fountain (and no one else is invited!).

I guess the cigarette equivalent was thinking about smoking an entire pack, one after the other...

And my mind would play tricks on me as well.
Oh, that was terrible. I deserve a cigarette, don't you think? Just one, can't do any harm. After all, nothing that bad could ever happen to me again, this is a special situation. If I don't calm myself down with a cigarette who knows what I'll do!

Yeah. Anyway. I don't pretend to know exactly what would go through someone's head if they were addicted to cocaine, or that this is the same for everyone, but that is how addiction/cravings seem to work for me anyway.

A former addict's first response to stress is going back to his addiction.
The whole idea of kicking a habit for any reason (health, ethics, whatever) seems ridiculous when shit hits the fan. A quarrel with your partner is enough, let alone being accused for murder.
"If the world's so f...-up what's the sense in quitting?"
So, you might want to stress how hard it is for him to go without c. when the bad things start to happen, not only during this interrogation.

As for the interrogation itself, this is what I'd do:
I'm not my regular self now. On cocaine I acted cool and rational. Now I'm all nerves and ready to blunder. If I don't want to f-up this thing, I need to get some cocaine out of him first. It's more important than some health or whatever.

He would definitely taste the cocaine, I think. That's one way of your mind tricking you into enjoying a substance again after you've broken an addiction. He'd get the taste of cocaine dripping from his nose into is mouth. It's an acrid, almost aspirin-esque flavor that is very pleasant (although it doesn't sound so) to cocaine enthusiasts. My guess is his heart-rate would also increase, and he'd feel vague flashes of being high -- again, all on account of his brain trying to simulate the stimuli that had appealed to him before he quit.