I am assuming you have set up DOSBOX correctly and that you are not looking for the password but the name of the program you want to run.
From the Dosbox command prompt -after you have mounted the drive your dos programs are on and changed the the directory to that drive - a dir should show you the directory of the program. If you then change the directory to that directory and run a dir you should see all of the files in that directory. If there is only one .exe that is the one you are looking for.
If you are looking for a password I cannot help you.