What is the maximum rated power of a flip-flop?
Most folk would assume that the chip is adequately soldered to a PCB that will conduct heat away without much of a local temperature rise (maybe a couple of degrees). So, use the "junction to board thermal resistance" (77.6 °C/W) and read the linked document (Semiconductor and IC Package Thermal Metrics application report) listed on the data sheet to understand how this works.