Need help first time visit to Switzerland

"Paris to which station is best to arrive? - the best station to arrive at is wherever you want to go in Switzerland. Where will you be staying the first night? That s the station you want.
Will you be starting in Central Paris, or direct from Disneyland? If you are starting from central Paris, trains to Switzerland depart from Paris Gare de Lyon. Disneyland has its own station "Marne-la-Vallée - Chessy", if you are starting from here you may not need to go via central Paris.

If you want to stay in one place (and you only have 4 nights, so I think you should), I suggest somewhere on the Jungfrau region, Wengen, Mürren, Lauterbrunnen or Grindelwald.

If you are going from the Jungfrau region to Milan, the quickest route is not via Lugano. Or do you want to visit Lugano?

Thanks for reply.
I am boarding train from Disneyland Paris.
By staying in Jungfrau region I can explore chocolate factory at brick Mt Titlis glacier 3000 etc?
I don't want to visit Lugano. Which is best way to reach Rome?

"I don't want to visit Lugano. Which is best way to reach Rome?" - You can either take a train to Zürich airport, and fly from there to Rome, or take a train all the way.

In order to look up train times, you do not need to know the best route in advance, you just look up xxx to yyy on your prefered train timetable website, and it will tell you the best route.
The same applies to your trip from Paris, if you are starting from Disneyland Paris, you need to look up trains from "Marne-la-Vallée" to yyy. yyy is wherever you are staying in Switzerland, which you haven't decided yet.

If you are staying somewhere in the Jungfrau region, yes you can visit Titlis and other places as a day trip. You would again have to look up train times.

Take a train from Zurich or Jungfrau area via Milan?
Is there direct train from Disneyland station to Jungfrau area station? Which is the shortest route?
Swisspass 4 days enough I guess.

Can u please suggest me a simple itinerary to explore above places. Arriving on 4th July to Jaungfrau area leaving on 8th July.

"Is there direct train from Disneyland station to Jungfrau area station? Which is the shortest route?" - You are making this unnecessarily complicated. There is no direct train, but you don't need a direct train. You don't need to know the shortest route in advance, that is the answer you will get when you look up train times.
The Jungfrau Region is a region, each town or village has its own station. See the map here: http://www.swissholidayco.com/Public/Assets/User/images/Excursions/Swiss%20Travel%20Passes/Jungfrau%202016.gif
You will be using trains and cable cars to travel from one place to another in the Jungfrau region.

First pick one place in the Jungfrau region, for example Wengen, Mürren, Lauterbrunnen or Grindelwald. then go to the Swiss Railways website: https://www.sbb.ch/en/
And look up trains from Marne-la-Vallée to wherever you choose. That will show the quickest route, and show how many times you need to change.

"Swisspass 4 days enough I guess." - possibly, depends on what travelling you will be doing once you gte to Switzerland.
Other options, like individual tickets, or a Swiss half price card.
If you choose a Swiss pass, you would also need tickets from Marne-la-Vallée to the Swiss border. tickets

"Take a train from Zurich or Jungfrau area via Milan?I" - as I said before, you do not need to go via Zürich or Milan.

"Can u please suggest me a simple itinerary" - you need to research the Jungfrau Region, and decide which places you want to visit, depending on your preferences.

I am trying to book hotel in Geneva for one night. Price shows very high. Some hotels are showing less price but swissborder, address shows France. I have to reach Geneva bus station Place Dorcière at 8.45am on 7th July. If I stay near Swiss border, cis it possible to reach at 8.45 am. ? How's the morning traffic in Geneva?

Traffic in Geneva during rush hour is not ideal. I just checked hotels for July 6 in Geneva and for Switzerland, they are not as high as I would have expected. I would book very soon. July 6 is a high occupancy date as the Jazz festival is during this time and there is high occupancy in the canton during this time.

My kids want to visit chocolate factory in Swizerland. Which is best route to visit from Lucerne? Any other chocolate factory other than in Broc?