This depends on what you are asking. If you simply want the value of the silver in the coin than whatever is the going rate for scrap silver. This is determined by the scrap metal market which is pretty much international.
If you want to get more money and the coin is in good shape/a rare/very desired collectible, you may be able to get more money. To get this kind of money you would have to sell to a dealer of coins, like a coin shop or a reputable pawn shop that deals in collectable coins.