Pepper Potts. She is very close to Tony and knows him well. She might notice some strange behavior or small signs that lead her to suspect he has hidden powers. For example, he might unconsciously use his powers in a moment of stress or danger when he thinks no one is looking.
JARVIS, or whatever advanced AI Tony has at the time. Since JARVIS is constantly monitoring Tony and his surroundings, it might detect some unusual energy signatures or patterns that are related to his hidden powers. JARVIS could then bring this to Tony's attention or, in a more interesting plot twist, start to act on its own to protect Tony's secret.
Bruce Banner. As another scientific mind and someone who also has a unique 'power' situation with the Hulk, he might pick up on some scientific anomalies in Tony that could indicate hidden powers. He could be analyzing some data related to Tony's health or the Iron Man suit and stumble upon something that makes him suspect there's more to Tony than meets the eye.
Maybe he doesn't fully understand his powers yet. Tony Stark is a scientific genius, but new powers might be beyond his current understanding. He could be worried that if he reveals them too soon, he won't be able to control them properly and might cause harm. So, he chooses to hide them while he studies and figures them out.
It could be Rhodey. As Tony's long - time friend and fellow Avenger, Rhodey would be eager to see him and would likely be among the first to be informed of his return.
In fanfiction, Tony Stark might have enhanced intelligence powers. He could solve complex problems at a super - fast speed, like coming up with new energy sources in minutes. His suit could also have new abilities, like teleportation. For example, he could zap himself from one side of the planet to the other to stop a disaster.
There could be some young and brilliant inventors like Peter Parker. His fresh ideas and quick thinking would be an asset to the team.
In the movies, Tony Stark's powers mainly come from his high - tech suits and his intelligence. But in fanfiction, his powers can be much more out - there. For instance, he might have the ability to merge with technology on a molecular level, which is not seen in the movies. This could give him the power to heal himself by using nearby tech components or even upgrade his body parts with advanced tech.
He could have the power of technopathy. Since Tony is already so connected to technology, as a mutant, he might be able to directly communicate with machines and control them with his mind. This would give him an even greater edge in creating and operating his Iron Man suits.
One great 'Tony Stark has powers' fanfiction is 'Powered Iron Man'. In it, Tony gains the power to manipulate energy on a molecular level. It makes for some really cool battle scenes where he can use his new power in creative ways along with his suit's technology.
Tony Stark might hide his PTSD in fanfiction because he doesn't want to be a burden. He's always been the one to solve problems, so showing vulnerability is difficult for him.
Hidden Midgard in a Tony Stark Avengers fanfiction could be a really cool concept. It might be a parallel dimension of Earth that has a connection to Asgard or some other alien realm. Tony Stark, with his curiosity, might be the first to suspect its existence. He could then use his Iron Man suit and all his tech gadgets to find a way to access it. Once there, he might find new allies or enemies, and this discovery could change the course of the Avengers' battles and their overall story.
Pepper Potts could be a big help. She knows Tony so well, and she could try to jog his memory by showing him things from their past together, like pictures or mementos. Rhodey could also be there for him. He could tell Tony stories about their military days and how they became friends, which might trigger some memories.