Open your System Preferences/Keyboard pane.
Click the box "Show Keyboard and emoji Viewers in menu bar."
Click on the menu item. Older systems will show a flag icon, newer systems show a an icon that has the old loopy Command symbol in a rectangle. Choose Show Keyboard Viewer from that menu.
An on-screen keyboard will appear. Press either shift key on your actual keyboard. On a (working) keyboard, both shift keys will highlight on the on-screen keyboard when only one shift key is pressed.
If you have tried your keyboard on several other computers, and you get no response from either shift key, then your keyboard has failed. Something about the encoding line for shift key has been damaged. Could be either shift key, but both share the same function, and you are just unlucky enough that both shift keys have been taken out.
Oh, you can use that Keyboard Viewer to test nearly all your keys for a response. You might even find that there are other keys that have also stopped responding, or could even be stuck. The keyboard viewer makes that easy to see.