[General] ..about your most memorable event on/during last summer vacation.

[wotcha]

1. Write a short essay about your most memorable event during last summer vacation.

2. Write a short essay about your most memorable event on last summer vacation.


Which one sounds better to native speakers?

 

[5jj]

... in the/your summer holidays (BrE) / vacation.

 

[SoothingDave]

"During your summer vacation" - if you mean during the period of time that the student was out of school. (We end school in early June and resume in late August here.)

"On your summer vacation" - if you mean while they went on some sort of trip or excursion. During my daughter's summer vacation, we went on a vacation to the beach.