Open terminal and login into docker with the account credentials that you created in dockerhub
docker login
Create a directory and place the dat file in there (example /home/venkat/local-wallet/wallet.dat)
Run the following command in the terminal ( this command will launch the container and you will be inside the container command prompt at root directory (/))
docker run -it -v /home/venkat/local-wallet/:/wallet srgannav/pywallet /bin/bash
NOTE: This could take a while to download, configure and install
home/venkat/local-wallet/ is your host folder that contains wallet.dat and we are mounting that into the container folder /wallet (I have created the container with /wallet empty folder)
So the contents of home/venkat/local-wallet/ will be visible inside the container /wallet
Run the following command to dump the wallet (from inside the container)