How much time can one expect to spend with a trainer?
 

I have heard 275 hours at Werner and two weeks at Schneider.

Do companies generally send trainer and trainee out in trucks with two bunks?

Or do they share one bunk?

Different carriers have different time frames, some as short as a week, others a couple months. While with Swift I had to have a minium of 42 days out with my trainer, ended up being about 2 months (A few days over 42 days). And yes, usually you will be put in a full sized sleeper with 2 bunks, but 2 bunks or not, be prepared to not bring more then you absolutely need, it's small enough space for one, let alone 2 people.

275hrs with Werner is about right about 8 weeks if you are newly licensed. If you already have experience the training period will be shorter depending on amount of experience.
The 8 weeks can be accomplished all in one shot, with one trainer, or you can take 1 week paid personnel time off (PTO) at the mid point. If you take the PTO you will more than likely change trainers for the second half of the training.
Werner tractors are all two bunks. However you will use only the lower bunk when "team" driving. Best bet is to bring a sleeping bag and your own pillow. Thats the easiest way to move from top bunk to lower bunk. Usually the lower bunk is the Trainers when the truck is stationary, the trainee will be relocated to the upper bunk.
Like matcat said. Bring only the minimum with you. You may or may not have shelf space available to you. Some trainers allow shelf space some do not. I found it easiest to just keep all my necessities packed in my suitcase at the foot end of the upper bunk, secured with bungee straps.

I was fairly lucky to get a trainer that was really cool, had a lot of experience, and kept space open for you to put your stuff, like Drew10 said as well, usually the trainer will keep the bottom to himself, but when you are team driving, you are required to sleep on the bottom bunk for safety purposes, and believe me, it can be a bumpy ride trying to sleep in that sleeper when the truck is moving. I can remember quite a few times waking up halfway in the air between the bunk and the bottom of the top one :P (This is why they have safety net to use while sleeping, but I never used it).

with USA, it was around 30 days with a trainer, You had to have 175 hours driving and complete all the lessons in your workbook, have your trainer sign off on you, then you could come to test for first seat driver.

SNI is 2 weeks minimum, more if they feel you need it.
I would not be a truck driver if i had to spend more than 2 weeks, much less 2 months with a trainer.
F that in the A.
I have no idea how they do it.

Time With A Trainer
 

Depends on the wagon you're draggin' and the company. Expect four to eight weeks depending whether a van or flatbed. the more specialized, the longer, more time spent with a good trainer is a good thing.
Do companies generally send trainer and trainee out in trucks with two bunks? Depends on the tractor, if it's a flatroof, one bunk two people. A condo, two bunks, but the top one isn't used (safety issue) if the truck is gonna be rollin' after the trainer feels the newb can drive w/o him being in the second seat watching.
Or do they share one bunk? See the flatroof comment, pack a bedroll or sleeping bag. BOL

As a newbie, I'm hoping to get a good trainer that will share his talents with me. If it takes me 4 weeks or 8 weeks, I just want to be ready for the road ahead.