Q: After restoring my iPhone 6s I don't have access to all of my music when I'm not hooked up to wifi. How do I fix this?

Settings - Music - check to see if Cellular data is turned off - toggle to on and see if that solves your problem

(1066)

Are you using Apple Music?

If so, then you need to mark the music you want to listen to offline. Follow the instructions in this support article under "Save Songs, Albums, and Playlists to listen to Offline":

Add music from the Apple Music catalog to your library - Apple Support

Cheers,

GB