Q: How to sync two devices on the same itunes account

Hello MissyKate,

I understand you are trying to sync your new iPhone 6 with the iTunes library on your computer, and you want to sync the same info that you have synced to your iPod nano.  

I do not seem to be able to sync all the content

Missy, what content is missing when you try to sync?  Are you getting any error messages?   If you have a playlist created for songs that you want on your iPod nano, you should be able to choose this same playlist for your iPhone 6.

The articles below explain how to sync with iTunes using a USB cable, or syncing over Wi-Fi.

Manage your associated devices in iTunes - Apple Support
https://support.apple.com/en-us/HT204074​

You can see if your Mac, PC, iPhone, iPad, or iPod touch is associated with your Apple ID in the iTunes, iBooks, and App Store, and manage your associated devices. Just open iTunes using your Mac or PC.

When you turn on iTunes Match, Family Sharing, or Automatic Downloads, or when you download past purchases on your computer, iPhone, iPad, or iPod touch, that device becomes associated with your Apple ID. You can associate your Apple ID with up to 10 devices, with a maximum of 5 computers at any time. Each computer must also be authorized using the same Apple ID. You don't need to authorize your iPhone, iPad, or iPod touch.

After you associate a device with your Apple ID, you can't associate that device with another Apple ID for 90 days.

 Sync your iPhone, iPad, and iPod with iTunes using USB - Apple Support
https://support.apple.com/en-us/HT201253​

Sync your iPhone, iPad and iPod touch with iTunes using Wi-Fi - Apple Support
https://support.apple.com/en-us/HT203075​

Take care,