The BIS Triennial Central Bank Survey shows that over the last three years the position of the dollar as key currency has become more dominant. The figure below shows the turnover by currency and currency pairs.
You can see that the dollar was on one side of the operation 87% of the time, compared to 84.9% three years ago. The euro has lost some ground. Also, the average daily turnover in foreign exchange markets in April was around US$ 5.3 trillion.