I have a Galaxy Note 4 (T-mobile) running the latest firmware and it's on Android 6.0.1.
When I say "Ok Google" to my phone locked screen, it'd wake up, but then I'd get stuck on the Lock Screen. I'd have to manually unlock it (I use the Swipe Pattern Lock). That beats the purpose of operating Google Assistant in a hands-free manner, especially when I'm driving.
The "Trusted Voice" option is missing from my Google Assistant/Now settings. "Ok Google from any screen" is available and is turned on. I remember back then I used to have the "Trusted Voice" option, but maybe in the last few versions, it's been removed? I'm not sure.