Do you mean it should hide all the other images when you select a mesh key?
If you mean the dopesheet should only show keys of your selected mesh, it already does that.
Just make sure the dopesheet is not locked. Look for the lock icon and make sure it's turned off.
Dopesheet - Spine User Guide: Contents
This is also unless you have several slots and meshes under the same bone.
The focus of the dopesheet is currently on the bone level, unfortunately.