No, you do not need a Poland Visit Visa if you already have a valid Schengen Visa. If you have a current Schengen Visa from another country in the area, you can enter Poland and travel within the Schengen Area as long as your visa is valid. Make sure your reason for travel and how long you stay follow the visa rules. But, if your Schengen Visa has run out or only lets you visit certain countries, you'll need to apply for a new one.