How to get the sketch block when I select one sketch line/point of it.

I have a sketch block with several sketch lines / points in it.

I want to get the sketch when user selects sketch lines or points of it.

But I donnot know when the user will select, so I cannot set the Selection Filter.

So, any method to get the sketch block when I get the selected line or point which belongs to the block?

Thanks very much for your tips!

SolidworksApi macros