Inside sketch mode (sketcher?), you need to right click a bunch of times on a groups of contstraints until you're presented with an option to select the one you want. If you miss it, you even have to go around the horn and start over.
Suggestion, move the contraints out so they're able to be selected with a single click. Make the "point on entity" like the "equal length" or the "vertical" contstraint.
