The class you would want to use to develop your solution is the DriveInfo class. There is no way to guarantee it is the same drive easily but you can use options such as the DriveType property to check it is a removable USB drive or the VolumeLabel if you are trying to make it only use one USB stick.
DriveInfo allDrives = DriveInfo.GetDrives();
foreach (DriveInfo d in allDrives)
if (d.DriveType == DriveType.Removable && d.VolumeLabel == "VolumeLabel")
FileInfo file = new FileInfo(all_path);
file.CopyTo(d.Name + @"\data\testing");