All Y-20s so far (including prototypes and in service airframes) are all powered by D-30s; we haven't seen WS-20 on any yet. We'll see Y-20s being tested with WS-20s before we see in service Y-20s powered with them.
Right now there are two in service Y-20s positively identified, with numbers 11051 and 11052. We don't know if there's anymore that have been produced for the same unit.