When you select an audio event in the "Edit screen", the wave form is shown in the "Audio clip display" and the marker on the wave form moves corresponding to the playback position of the audio event. Place the cursor on the "Audio clip display" where you want to split the event. Select "Play one audio event" (Return) in the "Control" pull down menu and it will playback from that point. If the position for the split is not correct, you can adjust it with the Right and Left Arrow Keys.
Once you have set the correct position to split, select "Split audio event" (Ctrl+S) in the "Audio event edit" pull down menu. When the confirmation message is shown, click "Yes" to complete the split.
The 'Split audio event' button in the tool bar
Right click on the 'Audio clip display' to specify the split position
