How can I start a new pen path from existing anchor point of a already CLOSED shape? (Adobe Flash)
Deselect the shape if you've just drawn it (I find the quickest way to do this is tap [V] to enable the Selection Tool, then [P] the enable the pen again), then mouse over an anchor point on the path. You should see the little symbol next to your pen cursor change to a diagonal line. Click once, and then you can continue drawing.