Here is the full list of all 26 GNOSIA achievements.
All skills acquired
Won while playing as an Engineer and discovered the Gnosia three times in one loop
Won while playing as the sole Gnosia with 15 crew members present
Won while playing as Human under "6 Gnosia" conditions
Reached the true ending
Reached the ending
All Setsu special items unlocked
All Remnan special items unlocked
All SQ special items unlocked
Entered a world with 0 Gnosia
Won while playing as a Bug and announcing your role under unfavorable conditions
Won while playing as an AC Follower and announcing your role under unfavorable conditions
All Yuriko special items unlocked
All Gina special items unlocked
All Otome special items unlocked
All Raqio special items unlocked
All Jonas special items unlocked
All Kukrushka special items unlocked
All Stella special items unlocked
All Shigemichi special items unlocked
All Chipie special items unlocked
Won while playing as a Guardian Angel and succeeded in protecting a crew member twice in one loop
All Comet special items unlocked
All Sha-Ming special items unlocked
All roles unlocked
All crew members appeared