In a legal case, discovery means evidence/data https://en.wikipedia.org/wiki/Discovery_(law)

This person was probably writing scripts/tools to grab data from email servers, databases, code, etc.

In this context I imagine it's primarily the collection and collation of play logs.

I take it that "discovery" is the process of communicating with the people who are suing providing the raw data and facts as to their basis for suing. This could be a giant spreadsheet of the songs that were sold and what was paid on it.