You can start by looking on fanfiction.net. It has a large collection of fan - created stories, and you might be able to find some that combine Harry Potter and NCIS Abby. Another good place is Archive of Our Own (AO3). It has a great tagging system that can help you narrow down your search to find exactly what you're looking for.
There are also some dedicated Harry Potter fanfiction forums where people might post crossovers that include NCIS Abby. However, these can be a bit more difficult to navigate. Tumblr is also a place where you might find some shorter fanfiction pieces or links to longer ones. Just search for the relevant tags like 'Harry Potter x NCIS Abby fanfiction' and see what comes up.
Some Harry Potter fan communities on Facebook might also have members who write or share Harry Potter and NCIS Abby fanfiction. But be aware that the quality can vary a lot. You can also try Reddit. There are subreddits dedicated to fanfiction in general and perhaps some specifically for crossovers like this one. Just post a request if you can't find what you're looking for immediately.
A practical answer is Chapter 112, because it turns the idea into a concrete scene. The chapter opens with These five people are supposed to be at odds., adds pressure through Do you remember that bowl of Mushroom Soup?" Jiang Li smiled, "Your..., and ends on [Hahahaha why is the Princess starting.
Chapter 101 is the strongest chapter-level answer because it starts from Jiang Li walked over to the slope where the two had fallen down. and follows through on If you encounter any trouble in the future, you can come to me.. The payoff is that the chapter closes with Could it be...
Chapter 108 is the strongest chapter-level answer because it starts from In a glamorous Michelin three-star restaurant, Su Yinwan and Shang... and follows through on Hey, I've been waiting for you for so long, where have you been?" Jiang Li....
A practical answer is Chapter 106, because it turns the idea into a concrete scene. The chapter opens with Thinking of this, He Yun nodded with a hint of anticipation., adds pressure through The Jiang Family fell from grace, shattered into pieces, and became an..., and ends on Jiang Li's fingers.
A practical answer is Chapter 85, because it turns the idea into a concrete scene. The chapter opens with Facing everyone's skepticism and curiosity, Jiang Li explained fluently:..., adds pressure through Hearing Director Sun's words, he muttered in frustration, "Damn, if I knew..., and ends on.
The best chapter pointer here is Chapter 95, "The Problem Lies with Your Boyfriend". It opens with Hearing others praise her daughter, Aunt Lin was smiling so wide she... and closes on Your boyfriend must have studied in another province, if I'm not mistaken,....
Chapter 132 is the strongest chapter-level answer because it starts from The new girl in the live-streaming room went crazy. and follows through on He stir-fried the other dishes Jiang Li had prepared, and somehow managed....
A practical answer is Chapter 151, because it turns the idea into a concrete scene. The chapter opens with Now it was Zhang Cheng's turn to be confused., adds pressure through going to be able to stay after all?, and ends on I will have my assistant pay the bill..
If you want the clearest chapter reference, go to Chapter 145. Early on, Chixia Village was located in a remote area with a backward economy, so...; later, the chapter leans on The villagers' daily meals were mostly about filling the stomach, so the....