I want to bid on an item in German ebay, and the currency is Euros. When I place my sniping amount, for example, $20, does that mean I'm bidding 20 Euros or 20 USD?
In your example you would bid 20.00 and eBay will accept that as 20.00 Euros (if the auction is in Euros).
One little suggestion? Don't bid 20, instead make that 20.12 or some other odd amount. That may be the difference between a win and a loss. You may be surprised how many times you can win by just a few cents.