Federal Cybersecurity Workforce Assessment Act - Requires the head of each federal agency to identify cybersecurity workforce positions within the agency, determine the primary Cybersecurity Work Category and Specialty Area (CWCSA) of such positions, and assign the corresponding Data Element Code.

Directs each agency head to establish procedures to: (1) identify open positions that include cybersecurity functions, and (2) assign the appropriate employment code to each such position and to each agency employee who carries out cybersecurity functions.

Directs each agency head, beginning not later than one year after such employment codes are assigned and annually through 2021, to submit a report to the Director of the Office of Personnel Management (OPM) that identifies the CWCSAs of critical need in the agency's cybersecurity workforce and substantiates the critical need designations.

Requires the Director to: (1) provide agencies with timely guidance for identifying CWCSAs of critical need, including current categories and areas with acute skill shortages and with emerging skill shortages; and (2) identify Specialty Areas of critical need for the cybersecurity workforce across all federal agencies.

Directs the Comptroller General (GAO) to analyze, monitor, and report on this Act's implementation.