When you use the term " Clip" I assume this is a short chunk of audio within a "track" right??. So a "track" made up of a bunch of "clips" will be handled differently than a complete "track" that is one long file.
To adjust the volume of a track is of course pretty obvious unless your really ne to DAW software.
You can also automate this both in real time or by inserting NODES ( right click)
If your talking about one little clip being to loud or to quiet you can just add the NODES to that little clip. SOnar does not include a wave editor but if you have one you can also use the Tools menu to open the clip in say Wave LAb or Audacity and change the volume there. Sonar has a audio volume plug but it will take a mono track and make it stereo..:(