To watch the NCIS three-part crossover involving NCIS, NCIS: Hawaiʻi, and NCIS: Los Angeles, follow the on-air order recommended by CBS for that event: Direct recommendation:

• Start with NCIS season 20 episode that begins the crossover (the first part of the event aired on NCIS, often titled with the episode number that starts the arc).
• Then watch the corresponding crossover episode on NCIS: Hawaiʻi (the next part of the story).
• Finish with the NCIS: Los Angeles episode that completes the crossover arc.

Notes:

• The three-part crossover is designed to be watched in one continuous sequence, as the narrative flows from the NCIS flagship into Hawaiʻi, and then into Los Angeles. If you’re cataloging by air dates, place them in that order: NCIS first, Hawaiʻi second, Los Angeles third.
• If you want a precise exact episode list for your viewing, I can pull the exact episode titles and numbers for the current year’s crossover and confirm the order.