Can someone tell me about 35N AIT. What should I read to prepare myself before AIT?

There really isn't much to read. The course will teach you everything you need to know, that's why it exits. Most of the information in the course is either classified, sensitive in nature or would be wildly inappropriate to talk about in a public forum for a multitude of reasons.

It is probably one of the least physically demanding courses that the Army offers, it is completely schoolhouse based. 6 months long, you can be assigned day OR night classes. Very small base, even smaller amount of things to do for fun, which you won't really have to be worried about with the new TRADOC policies. 35N school is like college, except without any of the fun parts.

Don't drink. Don't think about drinking. Don't talk to your friends about drinking. Talk to your PSG, see if you can start a petition to push America back into 1920s era prohibition; just to show them how
much you aren't drinking.

Pssssshhhhhhhh, what else....running on the flight line is whatever, you get used to it. No, it's not the elevation; you're just a bad runner. Go to the gym, go get something that plays Netflix. Get a tattoo if you want. Call branch about assignments, yes you can do that. 2 people to a room, no more bay life. Don't give up Hawaii so you can go to Ft. Stewart with your AIT romance partner, or do, whatever floats your boat on that. Go to study hall if you need it, don't go if you don't need it. Be respectful to everyone, it takes no effort and goes a long way.

What exactly did you want to know?? Was there something that you had a specific concern about?

I retired as a 35N Instructor about 4 years ago. Most of what you will learn is classified, so I won't be able to tell you much, and you won't find much material to brush up on. However, since the material is now up to date (you will be taught exactly what the combat zone analyst does on a daily basis), in the mean time you can brush up on your skills with MS Office (specifically Power Point and Excel).

A few things from a former 98C/35N.
1. San Angelo (Where Goodfellow AFB is at) is not a tourist destination. There is a mall and a tiny Best Buy and that is pretty much it. Entertainment will be up to you, just don't go to the clubs and drink. It's not worth the trouble, don't risk it. I recommend the gym and an Amazon Prime subscription.
2. If it stings, bites, or stabs, GF AFB has it. We're talking Brown Recluses, Black Widows, snakes, and cacti that can punch right through the bottom of your boot (Google Horsecrippler cactus). So when you're doing 3-5 second rushes during training, I would recommend not diving face first into the ground without taking a second to see what you're going to land on.
3. Maybe learn the ranks of the Navy, Airforce, and Marines, as they are all stationed there as well. It would be pretty embarrassing to blow right by some Navy officer without rendering a salute. Personal experience there, those guys have too many different uniforms...
4. Look at your longer than average AIT time as a chance to learn more than you did in BCT. Armystudyguide.com is a great resource to use. It can really help you when you get to your first duty station and set you apart from other FNGs.
5. As far a class work goes... yeah that stuff is all classified. I'll say that I didn't use much (if any of it) outside of AIT but you still need to know it. There are tests you have to pass and failure can get you rolled back months or reclassified into a new MOS. So don't screw around.

Good luck! 35N was an amazing MOS choice and allowed me to travel the world and make the most of my Army experience.