The information about your open position, including the Liquidation Price is available on the bottom of the BTCMEX Trading page.
You can also make the calculations of the Liquidation Price using the Calculator on BTCMEX. You can find it in the "Place Order" window on the left from the Trading Chart.
Select the "Liquidation Price" to start your calculations.
Learn more about Liquidation in the BTCMEX official Trading Guide.