This is easy.

If you press the Print button on your Browser then all Tiddlers that are currently open on your desktop will print out.

NB the following content NOT yet working (as at Oct 2012):

If you are using downloaded copies of the manual in its most interactive mode - as workbooks to keep notes on client work (ICR) - then in order to print out all notes related to your client, you should use the Print ClientNotes function.