You can definitely do that with cocoascript!
If you have a file path:
let pathToFile = "/Users/kgutowski/Downloads/Testing2.sketch"
let url = NSURL.fileURLWithPath(pathToFile).URLByDeletingLastPathComponent()
NSWorkspace.sharedWorkspace().openURL(url)
or if you have the folder path:
let pathToFolder = "/Users/kgutowski/Downloads/"
let url = NSURL.fileURLWithPath(pathToFolder)
NSWorkspace.sharedWorkspace().openURL(url)