How can I generate a full waveform from my audio file in After Effects?
It depends what you mean by the full waveform on a single frame.

If you want to view the entire duration of your audio file on screen in a single frame, you can do this, assuming your audio file is shorter than 30 seconds:


Add the audio file to a comp. 
Apply the Audio Waveform effect to a solid in a comp. 
In the audio waveform effects settings, set the audio layer to your audio track. 
Set the Displayed Samples setting to the sample rate of your audio file (eg 44100). 
Set the Audio Duration to the duration of your audio file in milliseconds (1000 per second of audio). 
Set the Thickness of your waveform to 1, to show more detail.


You should end up with something like this:


Which looks pretty similar to the waveform as seen in Adobe Audition: