"Due Diligence: Company Information for Law Students" (by Matthew M. Morrison -- Law Library Journal, 2016) is an excellent article included here for reference. "Due Diligence..." includes references to many sources, some (but not nearly all) are included in this research guide.
This article states, "Many law students are placed with corporate law firms whose clients are overwhelmingly companies. While many law school courses focus on doctrine, students need to learn company information and where to find it."
According to a survey of 300 hiring partners (via a LexisNexis 2015 white paper, mentioned in the article), "Skills identified as important include: