Turntable ground wires are usually connected to the preamp, PORT does not contain a preamp therefore PORT does not offer a ground lug.

Ate you getting any hum from your setup if not you probably don't need to do anything.

I have not purchased the port yet. This is a pre-purchase question as usually there is a ground connection in an amplifier, but in this case like you mention I may not need a ground to the port and hopefully there will be no humming or buzz in the sound. Thanks again. 

it looks like your turntable has a preamp built in.  Make sure you use the ‘audio port’ RCA ports on the turntable, not the phono.

I have the same issue. I just noticed the buzz on my music hall turntable that’s connected to my Port. It has a built in amp, and I connected the cables from the audio ports to the Sonos Port. There’s also a phono/line switch on the back of the turntable that I switched to line. Is there another way to ground that wire on the Port end? Thanks!

You would want to ground to another device, such as a receiver, or even the wall, but not to the Sonos Amp.