The Fifth Season → The Obelisk Gate → The Stone Sky. All three must be read in order — the trilogy is one continuous narrative split across three books. The Fifth Season's structure is deliberately disorienting; this is intentional.
Jemisin uses second person ('you do this', 'you feel this') as a deliberate narrative choice — the 'you' creates an unusual intimacy and also serves a plot function that becomes clear as the trilogy progresses. It's unusual but most readers adapt quickly.
The Fifth Season, The Obelisk Gate, and The Stone Sky each won the Hugo Award for Best Novel in 2016, 2017, and 2018 respectively — the only trilogy to achieve this. Jemisin's achievement was historic: she was the first Black author to win a Hugo for Best Novel, and the first person to win three consecutive Hugos.