EC Giruno

The train service on the 'Gotthard route between Switzerland and Italy has been transformed in recent years, new infrastructure including the world's longest railway tunnel, has now been complimented by new trains.

So new that ShowMeTheJourmey has yet to travel by them, hence the lack of an insider guide and the images being some of only a handful on SMTJ that its writers haven't captured.
Hence this link to The information on the SBB website about travelling by these 'Giruno' trains.

If you’re travelling 1st class you can order from the full restaurant menu and have the food/drink delivered to your seat
Though be aware that it isn't complimentary.
Also it can be a good idea to check with the conductor when boarding whether this as at seat service will be available for your journey, if it isn't you will have to go the bar car to order food and drink.

These same meals are available to 2nd class passengers in the restaurant car – prices compare favourably to Swiss restaurants.

The restaurant service tends to be popular, so in Switzerland many passengers head direct to the restaurant coach when boarding.
So if you want to be sure of a place in the car, the best option can be to go direct to the restaurant and then move to your reserved seat after your meal.

A bar car selling hot, cold drinks, light meals and snacks is also available to all passengers.

When travelling to/From Italy:

Reservations are compulsory for cross border journeys between Italy and Switzerland, and for journeys solely within Italy.

When booking international journeys online or at stations, the reservation is included when booking a ticket and the ticket(s) you will be issued will be seat specific.

When travelling to/From Germany:

Seat reservations are optional on this route and the fees are €5.30 in 1st class and €4 in 2nd class.
Book a 1st class ticket on DB, the German national railways, booking service or at a station in Germany and the reservation is complimentary and included within the ticket price, but if you book online with SBB, Swiss national railways, the reservations won't automatically be included.

For journeys within Switzerland:

Reservations are NOT required for journeys solely within Switzerland by these trains – though they’re recommended, as these trains tend to be busier than non-international trains.
However, as reservations are optional when travelling between Swiss stations they're not automatically included when booking tickets online.

Using rail passes

If you will be travelling with a Eurail or InterRail pass valid in both Switzerland and Italy, you have to pay supplement/reservation fees prior to boarding these trains for cross border journeys.
If you will be travelling from Italy, the rail pass reservations can be booked at the ticket desks at major stations and you won't be charged a booking fee.
Though the Trenitalia ticket machines don't sell reservations for these trains.

In contrast if you book reservations in Switzerland - at a SBB Reisezentrum booking desk, you will have to pay a 11 CHF booking fee - in addition to the reservation fee.
SBB's online seat reservation service does NOT sell reservations for international journeys from Switzerland.
The reservations for direct journeys by these EC trains can booked, without paying any additional fees, on the website of Austria's national rail operator, OBB.
It's best not to question the logic of this and use the only option for booking rail pass reservations on these trains, without incurring any additional expense.
Though the steps to take on the OBB website aren't particularly obvious, hence this guide* to booking Eurail/InterRail reservations with OBB.

In contrast to the international journeys, rail pass users don't have to reserve when travelling by these trains on journeys wholly within Switzerland.
It can pay off to take a chance on finding a seat when making Swiss journeys, as the reservation fees are comparatively expensive.

These trains have bike racks for non-folding bicycles, but bike tickets must be purchased prior to boarding, they can't be booked online for international journeys, so will need to be arranged at the station, but it's best to avoid leaving this to the last minute just before boarding.
Look out for the bike symbols on the train's exterior, you'll need to target these coaches when boarding.