I accidentally deleted the Downloads bookmark, and I wanted to recreate it with the same icon, but I can't find it.
"Icons are located in
This answer is only partially correct. If one does a locate
So a more generalized answer would be... in various directories under
I don't know what a "downloads bookmark" is, so I can't address your specific issue any further.
More specifically, the default icons that the file browser is using (currently up to version 15.04) are placed in folder:
The icon for the download folder is