Use the Mixer to accomplish this.
The Mixer works at Audio Track Level and affects all the clips on the same Audio Track.
Read up on the mixer.Its very powerful and has many appliable effects and functions.
Just to clarify, you can't adjust the level of multiple tracks at the same time. Each track would be adjusted individually in the Mixer window. But it seems what you're asking is how to adjust the level of multiple clips in a single track. There's a difference, and Craig's answer is how.
I don't see "Craig's answer" that Jim referred to. I have a similar problem. Lots of clips on one track that all need to be adjusted. (the clips, not the track) They were imported from Final Cut and all of the audio levels for each clip are set to zero for some reason. In FCP there is a keystroke to adjust all of the clip audio levels at once. I would like to do the same in Premiere. Thanks.
I had made Feature Requests to "gang" several Track sliders, like one can with a mixing board. However, the Sub-Mixes handles that nicely, as was pointed out to me by Adobe.
Thank you for linking to that KB Article, as it was basically the answer that Adobe gave me, but I had never seen it explained so nicely.
I don't see "Craig's answer" that Jim referred to.
Shooternz is Craig. However, I'm not sure that answer applies in your case. What specifically do you mean all clips are set to zero?