Can I use the mobile pass to go to every destination?

What you mean with every destination?

Most European Countries are covered Ofcourse you can´t reach Beijing (China) or Murmansk with the railpasses as they are not in the validity area :)

You can reach more than 90% of Europe with a Railpass usually just few islands and smaller villages aren´t connected and you have to pay for a short distance on top.

For example Grindelwald or Lauterbrunnen in Switzerland can only be reached from Interlaken by rail. The Railcompany between Interlaken and Grinelwald/Lauterbrunnen doesn´t recognise the Pass and you have to pay for the short leg. (They offer a 25% discount if you get the tickets at their office in Interlaken and show them the pass)

I’m sorry. 

Where I’m living it’s complicated to receive mail, so I need to buy  the mobile pass and in the Eurail website there is one list of the countries where the mobile pass can be used (I hope I am wrong about that).

So, let me be more especific. 

I would like to do these trips using the mobile pass: Brussels to London, London to Paris, Strasbourg to Luzern, Geneva to Marseille. Is it possible? 

Yes all these route are covered but note that even with a pass you have to pay for reservation on some of the routes

Brussels - London 35€, London - Paris once more 35€ (Attention limited seats for Eurail especially in summer sold out :/ )
Strassbourg - Basel - Luzern can be done without extra charge :)
Geneva - Marseille depends on the trains you take can cost 10 or 20€  on top of the pass for reservations

If you have a fixed shedule for your journey you may get cheap advance fares.

I have already known that these routes were covered. The point is: Can I do them using the Mobile Pass or I must have the paper tickets? Because as I’ve said, I can not recieve mail where I am living now, te only way for me is to use the Mobile Pass.

These trains that I must do a reservation, can I do a class upgrade at the reservation moment? Is it possible?

If you also pay the difference between 2nd and 1st class. Only possible at the ticket office and can be quite expensive, since it's usually the difference between the full fares.

On the list of countries using Mobile Pass, it does not list Switzerland, UK, or The Netherlands.  But I read on the comments above that we can?  I’m a bit confused.

If you have a global pass in mobile form, then you can use it for all participating railway companies. See this summary table or check the individual country pages for more details.

Looking at one country passes:

There's no separate pass for the Netherlands; it's part of the Benelux pass (also available as a mobile pass).

There's no pass for the UK. There's a one country pass for Great Britain (which doesn't include Northern Ireland) and a one country pass for Ireland (which includes both Northern Ireland and the Republic of Ireland).

A one country Eurail pass for Switzerland doesn't seem to exist.