If you visualize multiple databases and you want to create identical plots for each database but have them placed in different visualization windows then you can either have VisIt copy windows on first reference or you can clone an existing window and then replace the database used in the new window's plots with a different database.
If you have already created multiple visualization windows, perhaps as the result of a change to VisIt's layout, then you can make VisIt copy the attributes of the active window to another visualization window when you switch active windows by enabling Clone window on first reference in the Preferences Window. To open the Preferences Window, choose the Preferences option from the Main Window's Options menu. This form of window cloning copies the plots, lights, colors, etc from the active window to a pre-existing visualization window when you access it for the first time. If you have already accessed a visualization window but you would still like to copy plots, lights, colors, etc from another visualization window, you can make the destination visualization window be the active window and then copy everything from the source visualization window using the Copy everything menu option in the Main Window's Window menu.
If you have no empty visualization window to contain plots for the another database, you can click the Clone option in the Main Window's Window menu to create a new visualization window with the same plots an settings as the active window. Once the new window has been created, you could visualize a new database by highlighting a new database in the File panel's Selected files list and clicking the Replace button.