Giratina locations — where to catch

In Hisui (Legends: Arceus)

• Turnback Cave — Static Encounter

In Sinnoh (Diamond, Pearl & Platinum)

• Distortion World — Static Encounter
• Turnback Cave — Static Encounter

In Johto & Kanto (HeartGold & SoulSilver)

• Sinjoh Ruins — Static Encounter, Event

Other games (4)

• Brilliant Diamond / Shining Pearl (Gen 8): Turnback Cave
• Sword / Shield — The Isle of Armor (Gen 8): Max Lair
• Ultra Sun / Ultra Moon (Gen 7): Ultra Space Wilds, Ultra Space
• Omega Ruby / Alpha Sapphire (Gen 6): Soaring In The Sky

Giratina — full Pokédex entry