Can I modify the volume of a shot in the timeline of Premiere Pro?
When you drag a clip into a sequence, PPro will show a video track (if there is video) and audio track(s) if there is audio.  If there is both audio and video, the tracks will be linked.

The volume controls are on the audio track, not the video track.  You can adjust volume both on a clip basis and on a track basis.  Buy volume is a meaningless concept on a video track (even if the video clip is linked to an audio clip).