The way to determine the shortest path between two thoughts is to Select the two thoughts, right-click the selection window and choose Select Path Between.
That will add the joining thoughts to the selection window.
In v8 and below there was a way to show the "central" thoughts in the brain, I think it was done by the number of child thoughts, connecting thoughts and ... dunno, stuff. Anyway, it's not available in v9 at this time (bear in mind that v9 is a from-the-ground-up re-write), and I'm not sure if it's planned or not. Might be a good question to ask.
It was a nice novelty for me, but I only used it a few times and that was it. I'm guessing re-adding this might not be a priority right now.
If this is something you think you'd use, it might be a good idea to describe what you want and how you'd use it (or see it being of value). That generally provides developers a better picture of the intended use case and if/how it fits into the current plan, and other forum members something to discuss/rally behind or provide alternate suggestions.