Hi-

I believe if all in one sketch, SW recognizes the common point between lines A and B as just that - one common point rather rather than 2 coincident points.

If you add line C in another sketch, then close that sketch, you can right click over the point and choose "select other". Then you can see the relations and choose either point. If it's another sketch, then that would be considered "coincident" rather than "common".

Curious why this is important to you . . . . .

Good luck.