Can application see all WIFI SSID?
Yes, an app can see all surrounding WiFi SSIDs with correct permissions.

This is the main use case for WiFi analyzer apps (not affiliated, just to show as an example, have been using one of the listed apps).

As for the permissions required, the already mentioned Wi-Fi scanning overview states:


Android 8.0 &amp; Android 8.1: any one of 


ACCESS_FINE_LOCATION
ACCESS_COARSE_LOCATION
CHANGE_WIFI_STATE

Android 9: all of


ACCESS_FINE_LOCATION or ACCESS_COARSE_LOCATION
CHANGE_WIFI_STATE
Enabled location services (under Settings > Location)

Android 10: all of


ACCESS_COARSE_LOCATION or ACCESS_FINE_LOCATION
CHANGE_WIFI_STATE
ACCESS_WIFI_STATE
Enabled location services (under Settings > Location)