How can I view jnt files on my macbook?

You could try to install Windows Journal Viewer on your Mac.

http://www.microsoft.com/en-us/download/details.aspx?id=20771

As most Windows programs, for running it without installing Bootcamp and a complete installation of Windows, you can simply employ the free program Playonmac, which usually works perfectly with most old programs designed for Windows XP:

http://www.playonmac.com/en/

A jnt file is a Windows Journal file. I don't think you can open it directly on your Apple computer without first installing Windows.

Ask your teacher to print the JNT to a PDF.