What is everything that has to be done in 19D school to pass? What do I need to do to be prepared?

As a SSG you will be given supervisory duties at the school so don't be surprised to be leading troops while in training.
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Be flexible - Being a reconnassiance expert requires you to adapt quickly without losing focus on the mission. Your PRIMARY mission is always being to REPORT locations where the enemy IS/IS NOT, while not being detected. A mindset of "Let's f**K them up!" will simply get yourself and team cut-off and killed. Knowing where your element died will only tell graves registration where to look for the bodies.
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Understand that as a 19D, regardless of your rank it is a learning position, Your enemy can think and will adapt to your actions. Know that the school will give you knowledge to use in the tactical environment, but have to teach yourself in the field to use those lessons.
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Navigation is Key. Practice using a map on the ground, while vehicle-mounted and in the air.
Use your subordinates, their strengths and plan to improve their weaknesses by talking to them informally.
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Discipline in the garrison translates to discipline in the field. Start at the lowest level of leaderships. PFCs should be 'in-charge' of PVTs/PV2s. Your SPCs should be placed where they can informally assist and show lower grades (and each other) How-To-Do-It.
Your first-line NCOs, your CPLs and SGTS, need to give orders, not suggestions. Their primary duty is to inspect, correct and approve the performance of their assigned troopers. They should know the location, training status and health of their soldiers.
The SSGs ensures his Scout Section can maneuver and conduct missions both as a section and in conjunction with other elements withing the scope of his mission parameters.
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Chain of Command (as opposed to discipline but hand-in-hand in its exersize) is another key. Adapt yourself to lead according to what works, but enforce a rigorous set of rules, in-line with the structure mentioned under 'discipline' above. Many garrison traditions such as in-formation reporting ("1st Squad All Present", or "Pvt Jones on Supply Detail"), marching soldiers to and fro (giving junior leaders the opportunity to give orders thus acclimatizing them and their soldiers to follow their orders) and inspections after performance of thejobs assigned to the soldier by their firstline supervisor.
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These points will help you adjust to your new duties at your unit plus will help you pass the 19D course. Be a leader in the field but listen and keep your ego in place in the classroom. Relax and learn.

"Have to" reclass to 19D? As Major Payne would say, "I see you have a little attitudinal problem needs some re-adjustin'."

It may be poor word choice or a misinterpretation by me. But if you "have to" got to 19D school, you are starting off on the wrong foot. Regardless of how you got to where you are, you are there now. Embrace it and set forth with a positive attitude.

Beyond that, preparation is pretty much the same for any Army school. Make sure you are in good enough shape to pass PT Test and HT/WT / Tape. Cav don't like no weak sauce fatties, so be ready to pass with flying colors.

Get the pCking list, make sure you have everything, double check it, then have your PSG triple check you. Make sure you have your orders and understand them.

As far as actual schoolhouse knowledge type stuff, it is a standard Army school. It is designed to make you pass. They will tell you everything you need to know. Just show up ready to learn - and DON'T ARGUE or insist that you know better. Regardless of whatever experience you have in the field, THEIR WAY IS THE RIGHT WAY. Because their way is what gets you a "go" at this station.....

Also, it might help to know "Fiddler's Green" ahead of time.

If you are a staff sergeant, then you shouldn't sound like a lil baby. Especially as a ninjago pilot...jeez kid