Jon Snow may have had an inkling Daenerys Targaryen would destroy King's Landing according to the Game of Thrones season 8 scripts. Daenerys' controversial power move occurred during the show's penultimate episode, "The Bells."
After the difficult defeat during the Battle of Winterfell, Daenerys turned her sights to King's Landing and the False Queen, Cersei Lannister. With no hope of surrender from Cersei, Daenerys prepared her forces consisting of the Unsullied, Dothraki, and Northmen. Prior to the siege, Daenerys' closest allies started to become worried about her ability to effectively lead the Seven Kingdoms. That doubt ultimately assisted in Daenerys' transformation into a rage-fueled Mad Queen.
When Daenerys' forces marched on King's Landing, the ringing of the bells was meant to announce Cersei's surrender. In the episode, Tyrion reminded Jon to call off the men when he heard the bells. Of course, this didn't work as planned since Daenerys continued to massacre atop Drogon well after the bells went off. The scripts available at the Writers Guild Foundation Shavelson-Webb Library in Los Angeles (via Insider) revealed that the discussion between Tyrion and Jon regarding the bells was intended to be longer. Tyrion stated that a million people lived in King's Landing so it's important for the forces to pull back if Cersei surrendered. Jon then proclaimed that "I don't think she's letting anyone surrender today" in which Tyrion replied by bringing up the innocent children in the city.
Based on the original Game of Thrones script, it seemed like Jon knew that Daenerys had the intention of destroying King's Landing with no regard for the innocent lives that she would be taking in the process. The line insinuating that Jon was aware that she would take no surrenders would have had heavy implications on him. It would have looked like he knew what she was planning and didn't take enough action to prevent the massacre. In addition, it would have made his reaction to Daenerys' fiery rampage less genuine.
When Daenerys ignored the bells and decimated King's Landing, Jon's raw emotion proved that he was truly disturbed at what transpired. He and Davos urged some of the men to pull back from the city but they too were caught in the carnage. These moments gave Jon the justification in his mind that he needed to kill his former lover as a way to protect Westeros. Jon ended up killing Daenerys in the Game of Thrones series finale and in turn, changed the continent's leadership structure. If Jon had any part in Daenerys' actions in King's Landing, he would have been seen as a hypocrite. Even the slightest amount of negligence would have made viewers perceive his actions differently so it was probably for the best that the series went with the shortened version of the scene.