There are many great ways to better understand the legal research process, especially and specifically regarding tax law. Look at the lists below to see the various ways to gain certified knowledge and best understand legal research from subscription research platforms.
Bloomberg Law BLAW Skills Center - Provided you have a subscription, you may be certified in everything from fundamental research to obtaining tax-specific certifications.
Includes: State, Federal, and International Tax Research Certifications.
Thomson Reuters Knowledge Center: Westlaw Legal Research Certifications - With a Westlaw subscription, you may be certified in a number of basic, essential, and even advanced legal research certifications, though none that are tax-specific (though the closest option to this would be the Transactional Research Certification).
Includes: Transactional Research.
LexisNexis Legal Research Course Certifications - A LexisNexis subscription gives law students access to Lexis Learn, where users may look through different modules to better understand LexisNexis's system though, unless an instructor has crafted a course for them to complete, there is no named certification title from the research and module completion.
HOWEVER, LexisNexis does provide LexisNexis University, where a number of refresher and introductory courses to their products are free to view and work with.