About 35 eur. They are a tad expensive. Know that seat reservations on Eurostar are limited (very limited on Amsterdam-Brussel-Paris route) , get them as soon as you have a concrete travel date.

Eurostars Amsterdam Paris, can be avoided by taking the IC to Brussels, and taking regional trains to Lille, from where you can get a TGV from 10 EUR per seat reservation.

yes i know till Brussels i can go with regional trains.even till Lille you said.then Lille-Paris with the TGV,for just 10 euro extra?is this price for the reservation,or because of the high speedity of the train?

There are domestic and international fares. Every company sets its own prices so it depends.

For a good overview: https://www.seat61.com/interrail-and-eurail-reservations.htm

Note the passholder quota on Eurostar services + TGVs out of Brussels. You must book those as soon as possible. Fortunately there are slower alternatives (except to London).

thank you very much  for your answers.

I have another question.last year I have used for the first time Interrail Global Pass 5 days within 1 month .I thought it was for 5 days between the time you go somewhere and you come back,and not for 5 time you can travel.so I have used just 2 days,and another 3 days are staying free on the pass.so my question is can get some restitution for these unused 3 days back,even if it’s a 1 year later?

No, these days are lost I'm afraid.

Thank you