Xjournal supports detecting your currently playing audio by querying Apple's iTunes application. You can have Xjournal detect the track each time you create a new entry window by enabling the Detect current music when window opens option in the Xjournal Preferences.
To do this, select the Preferences option from the Xjournal application menu. Click the General icon to display general Xjournal preferences. Enable the Detect current music when window opens option and then close the preferences window.
TIP: You can force an update of Music field by clicking the Get Music toolbar item.