Jemma Simmons shared what happened to her on the other planet in "Agents of S.H.I.E.L.D." Season 3 Episode 5.
Season 3 Episode 5 is entitled "4,722 Hours." According to Den of Geek, the episode saw Jemma Simmons tell Leo Fitz her six-month ordeal on the other planet. She said that after being vacuumed into the other dimension, she saw herself on a sunless and deserted planet.
Simmons revealed that she had come across a pool of water, inhabited by an alien life. The water enabled her to live until she encountered the astronaut named Will Daniels. The latter had traveled through the portal with a group of scientists in 2001, when the monolith was still owned by NASA. However, they learned that it had an evil force, killing each of them.
According to Simmons, the opening of the portal could be foreseen by analyzing the patterns and alignments of the stars and the planet's moons. She and Daniels had done it over months, but the failed, with them losing hope.
Simmons also admitted that she had fallen in love with Daniels. The flare sent by Fitz allowed her to get out from the portal leaving Daniels inside while distracting the entity. Now, Simmons wanted to open the portal again to save Daniels.
Meanwhile, Season 3 Episode 6, entitled "Among Us Hide" will shift the scene from Simmons' story to the team's pursuit for Grant Ward. According to Spoilers Guide, Episode 6 will see Lance Hunter and Melinda May as they go after Ward and Hydra. The episode will also see Daisy Johnson and Phil Coulson start to doubt that the ATCU may be hiding something from S.H.I.E.L.D.
"Agents of S.H.I.E.L.D." Season 3 Episode 5, "4,722 Hours," aired on Oct. 27 while Episode 6 "Among Us Hide" is set to air on Nov. 3.