We recently discussed what happened to Daenerys' body after she died in the Game of Thrones finale. However, this is far from the only question that remains unanswered. The fate of the Mother of Dragons, her legacy, her possible return, all these are topics that could form the basis of the ninth season, if the creators of the series decided to continue it.
1. Where did Drogon actually fly and what does Bran want from him?
The last surviving dragon, Drogon, flew away in an unknown direction after Daenerys' death, presumably to the east. However, King Bran Stark immediately declared that he needed to be found. Why would he do that?
There are several possible options. The most obvious: Bran fears that such a powerful creature could threaten Westeros in the future. But there are more interesting theories. As the Three-Eyed Raven, Bran has the ability of a warg, perhaps he intends to subjugate the dragon. This has never happened in the history of the Seven Kingdoms, but who knows what new facets of magic will be revealed in the future?
In addition, the very fact of Drogon's existence destroys the idea that dragons have been lost forever. If there is at least one living dragon, perhaps there are ways to breed new ones. Season 9 could explore this, especially if there's a new claimant to the Iron Throne with Targaryen blood on the horizon.

2. Could Drogon find a new rider?
Dragons are known for their ability to change riders, and there have been instances in history where the same creature served different Targaryens. For example, Balerion the Black Dread first belonged to King Maegor and then to Viserys I.
Drogon was incredibly attached to Daenerys, but what if time passed and he took on a new rider? Someone with Valyrian blood (or even without it) could try to establish a bond with him. Perhaps there is a person in Essos who can tame him, this could completely change the balance of power in the world.
If season nine reveals a new rider for Drogon, he could become a new threat to Westeros. Perhaps the mysterious pretender will try to rebuild the Targaryen empire based on the traditions of old Valyria.

3. Did Daario Naharis learn of Daenerys' death and what did he do?
In Season 6, Daenerys left Daario in Meereen, entrusting him with maintaining order in the region. After that, there was no word from him.
Daario loved Daenerys. He was her most loyal supporter. It is possible that at some point, news of her death reached Meereen. But how would he react to it?
If he decided that his life was meaningless without her, could he focus all his efforts on revenge? For example, try to raise an army and go to Westeros to overthrow the new regime? Even if his chances of success are slim, the very fact that he appeared could create problems for Bran and his council.

4. How did Jon Snow cope with Daenerys' murder?
Season 8 left the most important emotional question unanswered: how did Daenerys' murder affect Jon?
We know he didn't do it willingly. He was convinced he was doing the right thing. But what did he feel afterward? He killed the woman he loved and the only person he could have ruled with. Does he feel remorse? Or does he perhaps convince himself it was inevitable?
Season 9 could have shown his internal struggle. Perhaps he would have started dreaming about Daenerys, wondering if it was worth it?

5. What legacy did Daenerys leave behind?
After all her conquests, all her battles, and all the people she liberated, how is she remembered around the world now?
In Westeros, she is likely remembered as the "Mad Queen" like her father. But in Essos, things could be different. In Meereen, Astapor, and Yunkai, she could be remembered as a liberator, and if Season 9 brings new conflict, there could be people ready to avenge her.
For now, Season 9 of Game of Thrones remains a fan dream. But if it were to ever happen, these are the questions that would need to be answered. Daenerys' story is far from over, and her shadow continues to loom over the world she tried to change.