How to say please pray for me in ecclesiastical latin?

Peto ut pro me ores/I ask that you pray from me.

1. How do you say pray for me in Latin?
2. What is the Latin prayer Oremus?
3. What is the difference between Ora Pro Nobis and Orate Pro Nobis?

How do you say pray for me in Latin?

In classical/liturgical Latin, it could be rendered as ora pro me / orate (plural) pro me.

What is the Latin prayer Oremus?

Oremus (latin for “let us pray”)

What is the difference between Ora Pro Nobis and Orate Pro Nobis?

In the Latin version, you'll note that the section in which the Saints are invoked has two options for the response: "Ora pro nobis" and "Orate pro nobis." The first is used in response to the invocation of a single Saint; the latter is used in response to the invocation of more than one Saint.