No wifi diagnostics in high sierra
How do I access the wifi diagnostics button & assist me in high Sierra?
Mac mini, iOS 11.3.1
Question marked as
According to this page (and my own testing):
https://support.apple.com/en-us/HT202663
you press and hold the Option key on your Mac, then click on the Wi-Fi status menu 
in the toolbar
specifically:
Analyze your wireless environment
Your Mac can use Wireless Diagnostics to perform additional analysis.
- Quit any apps that are open, and connect to your Wi-Fi network, if possible.
- Hold down the Option key and choose Open Wireless Diagnostics from the Wi-Fi status menu .
- Enter your administrator name and password when prompted.