Be onto
Pursue, be aware of someone's true nature
Fasten onto
Follow someone closely, normally when they don't want your company
Front onto
Face (of a building)
Get onto
Start discussing a topic
Give onto
Open into a place, for a door or window
Hang onto
Keep
Hold onto
Keep as long as possible
Latch onto
Connect to something
Lock onto
Find a target and head for it
Tack onto
Add or attach something that wasn't planned to something
Tag onto
Add an additional point to something written or spoken
Veer onto
Change subject to talk about something different