The release week of chapter 257 was one of the most exciting and confusing in Jujutsu Kaisen history, rife with major developments that had some minor mistranslations by leakers. However, with the official Japanese and English copies of the issue out, fans have all the official confirmed information they need moving forward.
For example, initial leaks had claimed Yuji himself was the reincarnated soul of the twin whom Ryomen Sukuna ate in the womb during his mother's pregnancy. However, the official release of the latest Jujutsu Kaisen chapter revealed it's Yuji's father, Jin Itadori, who was the reincarnated soul of Sukuna's twin brother.
While this and many more issues were cleared up by the official releases of the Jujutsu Kaisen manga series, several questions still remain in the series overall. More specifically, the series has not answered two huge questions focused on Yuji.
Jujutsu Kaisen still needs to explain Yuji's physical appearance and ability to swap souls and enter inner domains
The first major question Jujutsu Kaisen still needs to answer concerning Yuji is his new physical appearance, namely his arms and hands. While they have some base similarities to those of Sukuna's, such as the elongated nails, they are largely distinct from Sukuna and anything or anyone else in the series in terms of appearance.
More likely than not, this results from Yuji being the son of the reincarnated soul of Sukuna's twin brother. This theory would explain why his arms and hands share some slight similarities to Sukuna's but are distinctly different. It would also help to explain why Yuji being the son of Sukuna's twin brother is so significant, possibly revealing that Yuji's appearance is what Sukuna's twin brother may have looked like.
His arms changing being a result of his origins in Jujutsu Kaisen could also set up an explanation as to why Sukuna killed his twin in the first place, which he isn't even sure of himself. If it were revealed that Sukuna's unborn twin was already manifesting power equal to him in the womb and Sukuna instinctively killed him likewise, it would also explain Sukuna's inherent disgust and hatred for Yuji's existence.
The second of these two major questions is how Yuji's ability to enter a person's inner domain and seemingly swap souls with them works. The latter point is especially intriguing since it doesn't seem related to the "target" having a Cursed Technique. This theory was proven true when it was revealed that Kusakabe and Itadori swapped bodies, yet it was also confirmed by then that Kusakabe does not possess a Cursed Technique.
However, the answer to the former will also likely answer the latter point, with the two Cursed Techniques Yuji has engraved in him currently not answering how he does this. While he may possess a third Cursed Technique, which is uniquely his own, this explanation doesn't seem likely, given how the series is currently progressing.
More likely than not, the answer will build off of Yuji's origins as the spiritual son of Ryomen Sukuna's twin brother. It'll likely be revealed that Sukuna's twin possessed an innate ability to access and understand their own soul and the soul of others. This explanation would also provide a callback to Yuji telling Mahito he was just like him during the Shibuya Incident arc since Mahito's powers also revolved around the outline and form of one's soul.
Related links:
Jujutsu Kaisen chapter 258 official release date and time
Jujutsu Kaisen chapter 257 highlights