The code looks like this:
// Play a running animation on track 0, and a shooting animation on track 1.
skeletonAnimation.state.SetAnimation(0, "run", true);
skeletonAnimation.state.SetAnimation(1, "shoot", false);
The spine-unity docs may be helpful for you.
http://esotericsoftware.com/spine-unity#TRACKS
http://esotericsoftware.com/spine-unity#SpineAnimation
Keys on the higher track will override keys on the lower track. So you can structure it however way you want in that context.