if Google Now on Tap (Android Marshmallow or better) doesn't turn on or turns on, but quickly turns off, then you probably have an account on google apps. Your domain administrator needs to do the following (referenced from: https://productforums.google.com/d/msg/websearch/hLazcAVC5MA/0kV53XllqFkJ)
open admin console (admin.google.com), then choose Apps, then Additional Google services. Then disable filter "Top featured services" near the top half of the page. This is important (!). When you turn filter off you will see a long list of google services, you have to find "Web history" and turn it on.