In an Alternative Universe when everyone knew Jon was a Targaryen + the Targaryens still were sitting on the Iron Throne, who was in the first line to rule next? Jon 或者 Daenerys?

Jon probably. Aerys was the king, Rhaegar was the crown prince so Rhaegar's son would come 下一个 in the line and since Aegon is dead, that puts Jon 下一个 in line for the throne. But Jon's claim could be weaker if Rhaegar and Lyanna weren't married.

So in short, Jon is the heir to the Iron 王座, 宝座 if Rhaegar and Lyanna were married. If not, then Jon is still a bastard with a weak claim and Daenerys has a stronger claim.

Jon would be 下一个 in line if his parents did marry 或者 if he was legitimised 由 the king. A legitimate child comes before a sibling - siblings are only heirs if someone has no children/only bastards.