If Schoolrunner detects that students are linked, you'll be able to see these connections at the top of the student "Contacts" tab in the Schoolrunner 2.0 mobile app.
If you log a communication for the student, you'll see that linked students are selected by default. You can remove any/all of these students by tapping the orange "linked students" button.
Fill out details about the communication as usual. When you save, identical records will be logged in Schoolrunner for each student that remains selected.
Note: like linked students in the website, any linked students that are at other schools will be included on both the "Contacts" screen and on the "Log Communication" screen.