Q: Itunes will not sync with my iPhone 6s and my make book pro

Hi,

You must be using the same Apple ID on both the iPhone and the MacBook Pro in order to sync iTunes purchases.

To see which Apple ID is used on the iPhone, tap Settings > iTunes & App Store > Apple ID

On your Mac open iTunes. From the iTunes menu bar click Store > Sign In.

Sync your iPhone, iPad, or iPod touch with iTunes on your computer using USB

Also, on the iPhone, if you want to sync music directly with a Mac's iTunes library, turn OFF iCloud Music Library (if you have one).  The setting is on the iPhone's onboard Settings screen, under Music.