So basically I can see if my neighbours are surfing on porn sites regardless of WPA or SSL/TLS?

If you break their WPA, then yes, you can see which servers they connect to. For your purpose that possibly would be enough to know.

Regardless of WPA, no. Regardless of SSL/TLS, yes.

If the WiFi uses encryption, DNS is encrypted too.

Yeah but without wifi encryption, and with SSL you can still snoop on DNS traffic.