Work features cannot be created or edited in a sketch, but you can use the Project command on the Sketch tab to project them to a sketch.
To edit a sketch, double-click a sketch symbol in the browser to activate.
Projected work geometry is associative to the parent work feature. To modify the projected geometry (such as trim or extend it), break the associativity by changing the style from Reference to Normal.
You can delete projected geometry without changing the style.