I found a good spot to farm this trophy in chapter 5: Urban Warfare. You will need to platform around and over a building to let Chloe through and there is a good spot in the video for farming grenade kills and kills from a hanging position. Just suicide to rinse and repeat.
This is just after Chloe has fired the rocket launcher and you meet up for the first time in the chapter.
If you don't have any grenades approaching this point there is one on the washing machines near where Chloe waits for you.