if you play the video on the laptop and you can hear the sound out of the laptop speakers that probably means the default audio device on the laptop isnt HDMI.. if so, try looking at audio output settings and selecting HDMI as the default device..

"nVidia" is probably the device which generates the HDMI output, so it would normally be the appropriate choice to get the computer audio to play out via the HDMI o/p rather than through the (normal) speakers/headphone o/p.
In vMix, the HDMI input will be provided by a captured device of some sort, which as far as I can tell you are already selecting in order to see the video. It may be that there was no audio on the laptop HDMI output when you created the input, which is why the audio subsequently doesn't show up even when you change the setting on the laptop.

First step, if it were my setup, would be to check the laptop HDMI by connecting it to a normal TV (which has built-in speakers) so you can hear whether the audio is present. Then connect the HDMI cable to the capture device on the desktop, remove the existing HDMI capture input in vMix and add it again (or select change to reselect it from the available devices) and make sure that it's showing audio as available. Finally, make sure that the audio is enabled (and not muted) for that input.