When you are in a Smartskin window and in Muscle Mode you can use the |<< (Previous Keyframe) and >>| (Next Keyframe) buttons to jump between Smartskin keyframes. They don't always sequence in a logical order, you may need to press the buttons several times to access all of them This will work if the bone you made the smartskin for has no constraint controlling its movement. If it does, you will need to open the Pose with that constraint and temporarily Edit the constraint'