I am a JAWS user who has taken over 30 courses in Canvas.
I cannot see your image but I can post some tips on how to get JAWS or any screen reader to work with uploading assignments.
First, anywhere on a website where you can drag and drop a file, doing so with a screen reader is easy.
Using Windows explorer, what they now call File explorer, find your file. Press Control-C to copy it or right-click or press the applications key and select Copy from the context menu which appears.
You've now pasted a link to that file on to the Windows clipboard.
Next in the site go to where it says upload or drag and drop and press Enter. You might also need to tab around to locate a Browse button. Canvas in some of these situations, depending on how the assignment was set up also has a tabbed dialog where you can choose whether to upload from your computer, your google drive or some other place. You have to find the right button and press space on it.
But eventually, you'll get a File open dialog box -- a standard Windows File open box. In the edit box for the filename, you simply press Control-V and your filename is pasted right there.
Next, you go to open and press Enter or Space. Then you tab over to submit.
Where it is confusing is the part when you are ready to upload the file. Typically a tabbed dialog is navigated with control-tab. But on the web you cannot do that. You have to tab around until you find the tab in the tabbed dialog, press arrow to move between tabs and enter to activate that tab. So if the tabs are to upload from your computer, google drive, or submit text, you have to be sure the correct tab in the tabbed dialog is active.
If everyone who had to help a screen reader user would simply put their mouse in a drawer and practice doing these things with the keyboard first, they'd be much better equipped to assist. I find all this much easier to do with Chrome rather than other browsers.
You should also be aware that JAWS has several modes. To simplify, one is for reading and one is for interacting with a web control, like the rich content editor. If the student is in the wrong mode, doesn't know how to activate the right mode or turn the wrong mode off, unexpected results occur.