Why are Zygote and Whatsapp asking for root? Since yesterday, WhatsApp and Zygote have been asking for root permissions on my phone via supersu. Apparently zygote is a system app.

Is this malware? Lookout scan came up clean.
It is unlikely for WhatsApp to need root privileges, and impossible for zygote to ask for it.

Zygote is an essential system component that is started by init process itself while booting, so it does implicitly inherit root privileges.
Matter of fact, zygote is responsible for starting every other app, be it system apps or other apps.

Having said that, these two apps (installed in your device that asks for root access) are strongly MALWARE.

If you have ADB, issue the command adb shell ps | grep zygote. (Or from Terminal Emulator as ps | grep zygote)
I believe the output will be two processes: one is the real zygote, and the other 'zygote' is part of a package name, which is a malware.