What is 35M AIT like?

I probably been to a few dozen schools and courses over the course of my career - some one day, some 6 1/2 months. Every single one of them taught me everything I needed to know to graduate/pass. All you have to do is LISTEN and DO WHAT THEY SAY. Seriously. In every single school, from 11B One Station Unit Training to 1SG/Cdr Pre-Command course, you are GIVEN ALL THE ANSWERS if you pay close enough attention.
35M AIT is no different. When they say make an interrogation book, MAKE ONE. When they tell you what questions to ask, ASK THEM. When they tell you to remember your "elses and others" REMEMBER THEM. And when they tell you to include something in your report, INCLUDE IT.

Aside from that, do NOT think of your "off time' as "free time." Think of it as "practice time" or "project time." You are in school in the middle of nowhere in the Arizona mountains. There is nothing better to do, anyway. Take the time to make your interrogation book, practice your questioning, rehearse approaches, etc. Get together with your roommate / classmates and form a "study group" and take turns playing roles and interviewing.

If you do what you are told, take it seriously, and work hard at it, you WILL pass.

11B / 35M, here.
In the Infantry I was taught battle drills in order to defeat the enemy wherever the battle may be i.e. in a field or inside a structure, on a mountain or in the jungle.

35M training required me to upend my entire understanding of a battle drill on it's head.
Instead of practicing how to shoot an enemy, provide them aide etc you'll approach the situation with your mind, words and personality.
This MOS is unlike Infantry in that in the Infantry we can usually discuss weapons and tactics. As a 35M you're not going to discuss anything unless in classified environment.

The best advice i can give you is "Practice booth hits" with your classmates as often as possible which should be every single day.

The first phase of 35M is DLI. You'll need at least a 107 DLAB or a 2/2 DLPT in a qualifying language, and you'll need your TS clearance prior to even being able to request a class seat. You'll need to start your clearance now because it can take a good six months or longer before you have an interim granted