Apple - How do I open the javascript console in Safari 6?

Open Safari and choose Safari > Preferences > Advanced. Then select the checkbox 'Show Develop menu' in menu bar.

Choose Develop > Show Error Console.

The console still exists, but it has moved.

Click the speech bubble tab at the top of the sidebar on the left side of the screen and then click on the Current Log entry in the sidebar.

The keyboard shortcut to jump to this tab is cmd+opt+c.

Note that the quick console is always available at the bottom of the screen and can be enlarged by dragging its top border upwards.

I recommend giving the About Safari Web Inspector a good read to familiarize yourself with the new Dev Tools.