No, technically you only need a reservation for the EC from Dommodossola to Milan. If you want to avoid that, like @AnnaB said, take a regional train from Domodossola to Milan (IR and R-trains, not EC).

But it’s kinda advisable to get them from Brig of course. You can get the reservations from ÖBB https://shop.oebbtickets.at/en/ticket . Do not select “seat reservation only”, but add to your passenger details the discount “Interrail/Eurail Global pass”.

Via this way you can reserve any train in Italy with mandatory reservations too.

Yes you can.

My crystal ball doesn't work very well :)

But it's in the middle of the week and there's no Italian or Swiss national holiday so I see no reason why it would be very busy.

Follow these steps:

(Note: Dommodosola should be Milano in my example)

The price. Eurail always adds a €2 booking fee per person and train and optional reservations are often already much more expensive to begin with. ÖBB don't add any extra fees.

Because it's cheaper.

There are many ways to book reservations, including various websites, by phone, at the ticket office, and you can indeed use what suits you. See this thread:

And this page:

https://www.seat61.com/interrail-and-eurail-reservations.htm

From Milano (Italy) to Venezia, the following schedule is listed on Eurail.com.
However, those schedule was not found on OBB.
Why is that?
I’d like to make a reservation on OBB. What can I do?
 

The Gotthard Panorama Express you mean? Do you have first classes passes or not?

It’s included, but you’ll need a seat reservation (and a class upgrade if you have 2nd class passes).

https://www.interrail.eu/en/plan-your-trip/tips-and-tricks/trains-europe/scenic-trains/gotthard-panorama-express

But you can easily do this route without any extra cost, by just taking ordinary trains. The views are the same.

Thank you very much.

1. What can I do with the following PE route? How can I make a seat reservation?
2. Also, How long would it take for the short transfer in Brig?

Thank you in advance.

This is the Glacier Express. It cannot be booked for such a short journey (or maybe at the prohibitive rate of 49 CHF).

Don't worry, there are 2 hourly trains from Zermatt (no seat reservation needed or even possible) : every hour at xx:13 and xx:37

However if your goal is Milan, no need to take the RE and change in Domodossola (unless you want to of course). Here is the best route :

- RE Zermatt - Visp 07:37 - 08:46

- IR90 Visp - Brig 08:55 - 09:02

OR

- RE Zermatt - Brig Bahnhofplatz 08:13 - 09:37

- enter the main building (easy)

- EC Brig - Milano Centrale 09:44 - 11:40

You book the seat reservation from Domodossola through tickets.oebb.at and that's it. If the journey doesn't appear on the app : either add it in 2-3 steps or manually. No need to do that in advance.

Thank you for the route you recommended. I’d take it. 

1. Is the 7 minnute transfer time enough from Brig Bahnhofplatz to Brig? (09:37-09:44 as shown below) How far is it? Can you show me the way for transfer?

2. What do you mean by “No need to do that in advance”? Do you mean that I can make the reservation even on the travel date or a day before? 

Thank you very much.

.

Sorry for the confusion. Adding the train to the app can be done at any point. It works like a diary.

However you need to make seat reservations in advance when required : through tickets.oebb.at for this route and all Italian trains.

The transfer in Brig is simple :

- arrival in front of the station

- enter the main building on your left

- go up the stairs or the ramp to plaftorm 4

I've done it a few times, although not with luggage (it shouldn't change much). I'd definitely do it. If you're worried, take the 07:37 train.

Thank you very much.
1.

In case I miss the planned train, which includes a paid seat ticket from Domodosola to Milan, can I take the next train, or should I buy another ticket?

2.
Can I cancel or change the ticket that I buy on OBB with Eurail discount if my schedule changes?

Any fees? If any, please let me know how much.

Thank you in advance.

1. If you miss it due to delays, speak to staff at Brig train station and they'll issue a new one free of charge. In addition you can always take reservation-free regional trains.

2. Seat reservations are generally non-refundable.

Thank you very much.

If I miss the train not due to the train delay but my fault (such as being late for transferring etc,), then will the the staff also issue a new one free of charge for the next train? Or else what should I do in that case?
 

You can take any train of each railway company that’s part of the Eurail/Interrail programme.

SBB and Trenitalia trains, all included. Each of their trains, from the smallest village to the biggest city you can take with the pass.

95% of all trains is included in Europe, some smaller (touristic) railways sometimes not.

See this overview of what’s included and not: https://www.interrail.eu/en/plan-your-trip/tips-and-tricks/trains-europe/railway-companies

For which date is this?

It could be that the ÖBB booking website hasn't been updated yet with the latest timetables.

It’s on 9, Aug., 
Then, should I wait until OBB is updated?

By the way, if I miss the train, for which I reserved a seat with Eurail discount, not due to the train delay but my fault (such as being late for transferring etc,), then will the the staff also issue a new one free of charge for the next train? Or else what should I do in that case?

That's indeed my suggestion. Those trains won't be fully booked m,ore than a day (or so) in advance, if ever.

If you miss your booked train by your fault, then normally you'll have to buy a new reservation.

Thank you.
In case I have to buy a new reservation because I missed my booked train by my fault, can I do it right at the train station? Would the tickets from Brig to Milano (actually tickets from Domodosola to Milano) be not fully booked on 9, Aug., on the day or a day before in general? 

There may or many not be seats left on the ECs from Brig on the day : the trains aren't that big and they can be pretty crowded in the summer. If you're alone, it shouldn't be a problem. 3 people (which I assume you'll be) shouldn't be an issue either but you'll likely not sit together.

There are always reservation-free regional trains available so if you miss the EC, this is the way to go.

- IR Brig - Domodossola 10:44 - 11:12

Then small stop in Domodossola, a nice town for a coffee :)

- R Domodossola - Milano Porta Garibaldi 12:01 - 14:14

- R Domodossola - Milano Centrale 12:56 - 14:35

The next EC is 3h later.

To Venice : the fast trains mainly leave from Centrale but there's one at 16:13 from Porta Garibaldi for example.

But don't worry, you surely won't miss the train anyway... :)

Thank you.
Panorama Express of Switzerland is not included, right?
What can I do to use the PE route with Eurail pass?
Thank you in advance.

For this route your Eurail pass is valid.

You can travel without reservations if you take a regional train from Domodossola to Milan. Otherwise you need a reservation from Brig (Domodossola) to Milan. Reservations on the Swiss part are only optional. 

Thank you.
I checked SBB site, but some of the time schedules on the SBB are not listed on the Eurail and/or OBB.
But then if a RE time schedule appears on SBB, can I use the route with Eurail pass?
Thank you in advance.

They have not the same update sometimes. To be 100% sure check the website of the train company that runs the train. 

In your case SBB in Switzerland and Trenitalia in Italy.

Thank you very much.
The time schedules shown on Eurail.com and OBB are different for my planned route. 
Why are they different? Which one is more correct?
If a schedule appears on any of the sites, that is a possible route?
Thank you in advance.