It is very hard to guess what are you doing.
From your screenshot we can see there is a directory /speedtest/ in the directory /mnt/ … But why? Did you created it with mkdir -p /mnt/speedtest?
Since the command ls is showing nothing, there is no binary to execute … It don’t look like you’ve extracted the downloaded file. I can’t say, from the given information, if you have downloaded the file or extracted it…

  1. Download the file on your computer
  2. Extract it on your computer to a new directory
  3. Copy the extracted directory to your router
  4. Login to your router
  5. Go to the file where you’ve copied the files
  6. Search the file ‘speedtest’
  7. Execute it…

And please give any command you are using, it is a lot more easy to understand.