When Did Jesus Appoint Clergy to Establish His Church?

Definitely before the Resurrection. Jesus calls Peter to be the leader of his Church (Mt.16:18-19) and ordains all of the apostles to be New Covenant priests at the Last Supper (26:26-29).

After Christ’s Resurrection, especially beginning on Pentecost, Peter and the other apostles begin to exercise their leadership roles in leading the early Church.

For more on this subject, please see my article “Pentecost and the Papacy.”