Jinshi doesn't know he's the current Emperor's son.
In the past he thought that he is, but it changed after his meeting with the former Emperor (iirc, someone can correct me if I'm wrong).
Jinshi was initially raised by the empress dowager with the story that he was the current emperor's son because the empress dowager specifically didn't want him to know that he was the pedo emperor's son. The empress dowager then revealed the situation to him when he'd grown up.
The problem is that the empress dowager didn't know about the baby switch. No one except a select few knows. There are three secrets about Jinshi being kept in the inner palace in increasing levels of secrecy:
1. There are three fake eunuchs: Jinshi, GaoShun, and his son Basen. Most people don't know this, but some officials associated with the empress dowager and some very old officials who've lived through the reigns know. Imperial officials close to the emperor also seem to know this. Aaduo of course knows. It is also possible that at least Consort Gyokuyou knows, although the other three (after Aaduo left) don't seem to. Rakan seems to know too but Maomao's adopted dad doesn't (because he was already kicked out of the palace when the subterfuge began)
2. Jinshi is the emperor's brother. This is known only to the emperor and his closest confidants, the empress dowager, and all the imperial rites officials. It isn't entirely clear Gyokuyou knows this. That is, she might know Jinshi's a fake eunuch but might not know who he actually is. One outsider (Maomao's adopted dad) knows, and it's possible Maomao's actual dad Rakan does too.
3. Jinshi is the emperor's brother. Only the emperor, Aaduo and her co-conspirators, the imperial secret service who uncovered the original baby switch, and Maomao's dad (who got punished then kicked out of the palace for not noticing the switch) know. The empress dowager doesn't know.