Select Cable Origin ⇧← – Logic Pro keyboard command of the day

  Select Cable Origin    ⇧←

Select the starting point of a cable.

Advanced selection commands in the Logic Pro Environment – Apple Support

Select Cable Origin: Highlights the source (or origin) object of a selected cable connection. This is particularly useful for troubleshooting, or when you want to make changes to a number of serially cabled objects (by changing the original).