Open your Final Cut project by selecting Open from the File menu.
Click the tiny Right Arrow at the bottom left of your Timeline window and choose Show Audio Wavefrom from the popup menu that appears.
Notice the audio waveform is now visible in your timeline.
Option+Command+W will toggle the waveform on and off.
If you want to show audio waveforms for every new sequence created select User Preferences... from the Final Cut Pro menu at the top left of your screen.
Choose the Timeline Options tab.
Check the box called Show Audio Waveforms and click the OK button.