iPod Touch Sync Now Grayed Out

Is the iPod touch set to sync to your iCloud Music Library, if you have one from a subscription to either iTunes Match or Apple Music? If so, you cannot sync directly with your Mac. You can check by going to the iPod's (onboard) Settings screen, then Music. The "switch" for iCloud Music Library is there.

If you don't have an iCloud Music Library, or you have one but it is turned OFF on the iPod, another reason for that Sync Now button being grayed out is Wi-Fi syncing is not enabled on the Mac (in iTunes). You need to connect it using a USB docking cable to set this up, on the iPod's settings screen in iTunes. There is a checkbox there for Sync with this iPod over Wi-Fi.