Torino, Italy to Gimmelwald, Switzerland

No such thing as a nonstop to Gimmelwald. For one thing, the only way to get there without hiking is by a bus from Lauterbrunnen then a cable car. And the train tracks to Lauterbrunnen are meter gauge, so a mainline train can't travel on them.

You will have to take a train to Milano, then a train to Spiez, then a train to Interlaken Ost, then a train to Lauterbrunnen, then a bus to Stechelberg, then a cable car to Gimmelwald. That is the minimum number of connections, and more depending on the time of day.

Probably best to book the Italian portion at http://www.trenitalia.com/tcom-en, and the Swiss portion at www.sbb.ch/en. And there are no sleeper trains.

You can take a train from Turin, Italy to Lauterbrunnen, Switzerland. It will likely have 3-4 changes and take about 6 hours. Sleeper trains are not likely available. The route will likely be Turin-Milan-Brig-Spietz-Interlaken-Lauterbrunnen.

From Lauterbrunnen you can reach Gimmelwald in about 30 minutes via a couple different routes. You can buy the tickets there or in advance.

As the others say, this will take multiple trains, each of which has multiple stops.
The phrase "nonstop train" implies to me you don't understand trains. Unlike planes, trains DO NOT just go from A to B. They go A, B, C, .... G, H. And they form a network, so at 'H' you change to another train to go onward to I, J etc.
And Gimmelwald is only reachable by a cable car, it is on the side of a mountain, and it is a small village with only 130 residents!
And there are no sleeper trains between Switzerland and Italy, but each of these trains is too short for a sleeper anyway.

Do not use a travel agency to book tickets, book directly with the company running the trains.
You can look up times, and see all the stops and connections, on the SBB (Swiss Railways) site: http://www.sbb.ch/en/home.html
However SBB does not offer all the cheap fares available on Italian railways. Once you have decided which trains to take, book from Torino to the Italian/Swiss border (Domodossola) on the Italian Railways site: http://www.trenitalia.com/tcom-en
And from Domodossola to Gimmelwald on the Swiss Railways site.

I'm sure you have your reasons by picking Gimmelwald, but I would recommend staying in either Lauterbrunnen or Murren. They offer more options for restaurants, and places to stay. You can walk through Gimmelwald if you want to see it; it will take about 10 minutes.

All of this information is very helpful in making my plans. Thank you very much for all of the responses!