Are you trying to find out what app a student first interacted with Student CRM? You can use the 'Source App' search in segments to find out which occurrence created the student, or you can look at their Student Record Card.
Source App in Segments
You can use the same filter below the line to build a more complex segment.
Using Student Record Card
You could also go into the student's Record Card and look at their "Source App" in the right-hand column.