Thank you all for your answers. 

I am making a detailed plan and calculation to decide which one is helpful. Thanks again for your input. 

@mcadv please don’t say things that are not always true.

You get around 15€ discount from the Sparschiene ticket like from 29€ in a seat. But Sparschiene tickets (Ticket saver tickets, or economy tickets, what ever) can go up to more than 90€ for a seat, than you have more than 15€ discount with interrail/eurail.

And don’t forget the standard fare Komfortticket. 

Please, repeating this claim does not make it a fact. You've been told numerous times that the discount varies a lot, depending on what other offers are available.

You mean the Swiss Travel Pass.

In fact the real discount you get with this suddenly so overhyped nighttrain is around 15€/ride, whereas a passday will cost around 40-50€. So it only makes real sense if you also plan to use the pass for more other longer trips.

Note that for extensive travel IN CH=Swiss there is also the Swiss Holiday Pass, cost a little more as IR-1 country, but is also valid on nearly ALL transit=the yellow postbuses, more raillines, also museums, and the discount on other mountain lines may be higher,

For the NightJet night train from Amsterdam to Zurich, OBB has a page about it here:

https://www.nightjet.com/en/buchung/tarifinformationen/interrail-eurail-paesse

Under the discount options when booking a ticket you select the "Interrail/Eurail - Globalpass" option and it will calculate the price you have to pay.

1. Yes it does. For a couchette or sleeper, reservations are mandatory and can be booked via ÖBB. Couchette from 44 EUR, sleeper from 74 EUR per person. Seats can optionally be booked for 4 EUR using the DB website.
2. Yes, you'll get a discount of 25%. You don't need a travel day to us a discount.

For just a return trip though, I'm not sure if the pass (4 travel days minimum) is worth the money. For travel with day trains, cheap (Super)Sparpreis tickets NL - CH can be booked via DB; for the night train, ÖBB has cheap offers if you book early enough.

Depending on what you're going to do in Switzerland and when you book, a pass may pay off. Rumour has it that a promotional pass offer will be available next month, so watch the Interrail website and do your calculations :)