You can find the Opening and Closing prices for your stocks by adding those columns to your Trader Workstation Watchlist or Portfolio pages. Right-click on the tab header and select Layout. Make sure you are on the Market Data Columns tab and find the Prices section on the right under Available Columns. Click the green plus sign (+) to expand the section. Click each price column you are looking to add, in this case, Close and Open, and click the Add button in the middle. You should now see those columns on the left side under Shown Columns. Once finished, click the Apply and OK buttons at the bottom of the window.
Alternatively, for instruments that don't provide Open/Close data, you can use the Time & Sales tool within TWS to refer to the pricing at a particular point in time.