Does Find My Friends require that Wi-Fi be on & that the app be running to get notifications? I'm not getting notifications from "Find My Friends." 


Do I have to leave Find My Friends always open to get notifications?
Does my friend's phone have to have Find My Friends open to send
notifications?
Do I have to have Wi-Fi on to get notifications?
Does my friend's phone have to have Wi-Fi on to send notifications?
No it doesn't have to always be open.
No, same as 1.
No, cellular connection works too. 
No, cellular connection works too.


Find my Friends would need permission from you to share your location as well as your friend. Once you two are sharing your location with each other, Find My Friends can send notifications that you have requested.