if you have trouble finding paths, add this code to frame#1
of any movieclip and it will trace its path in the output window -

trace(this);

if you have - mc1.mc2.mc3
and place the code on frame#1 of mc3, the output will be -
_level0.mc1.mc2.mc3

from mc3, if you want to reach the timeline of mc2 -
_parent.gotoAndPlay("a_label");

from mc3, if you want to reach the timeline of mc1 -
_parent._parent.gotoAndPlay("a_label");

from mc3, if you want to reach the main timeline -
_root.gotoAndPlay("a_label");
or
_level0.gotoAndPlay("a_label");