Open a file with spaces in the name in Terminal
Either escape the space with a backslash or use quotes.

open Test\ Subject.jpg




open "Test Subject.jpg"


You can also use autocomplete with tab. Type open Test then ⇥ to autocomplete.

Take note of the extension and make sure you use the right one. You've used 3 different extensions in your question, only the right one will open the file. List the contents of the folder with ls.